Online calculators, fast and complete

Work out a soil's available water capacity and the readily available water between irrigations from field capacity, wilting point and root-zone depth.

Science

Weigh the fertilizer dropped over a small test area and convert it to a rate per 1,000 sqft (or 100 m²) to dial in your broadcast spreader setting.

Lifestyle

Estimate a sustainable stocking rate and grazing days from pasture area, forage yield per area and each animal unit's intake.

Lifestyle

Use the nursery rule of gallons per inch of trunk caliper to get the recommended watering volume for a newly planted tree.

Lifestyle

Estimate daily reference evapotranspiration ET₀ (mm/day) from just max/min temperature, latitude and month using the FAO-56 Hargreaves–Samani equation — the basis for irrigation scheduling.

Science

From one nozzle's flow, ground speed and nozzle spacing, get a boom sprayer's application rate (L/ha or gal/acre) and the area a full tank covers.

Science

Enter the combined flow of all heads in a zone and the area they cover to get the precipitation rate (mm/hr or in/hr) and the run time needed for a target watering depth.

Lifestyle

Enter height and weight to get your BMI and category (underweight / normal / overweight / obese).

Health

Enter property price, down payment, term and rate — get monthly payment, total interest and total payable.

Finance

Cm, m, km, in, ft, yd, mi — common length units, converted instantly.

Conversion

Compute Ad Valorem Stamp Duty (AVD) on residential property at the latest rates.

Finance

Estimate Hong Kong salaries tax using both the progressive bands and the 15% / 16% two-tier standard rate (Year of Assessment 2024/25).

Finance

Hong Kong MPF contributions for employees, employers and self-employed persons using the statutory 5% rate with the $7,100 minimum and $30,000 maximum relevant income thresholds.

Finance

Estimate daily BMR and TDEE using Mifflin-St Jeor or Harris-Benedict, with calorie targets for cutting and bulking.

Health

From your date of birth, get exact age, Chinese nominal age (虛歲), days lived and days to next birthday.

Date & Time

Enter any two dates to get the calendar gap, working days, weekend days, plus year/month/day breakdown and total weeks/months.

Date & Time

Percent of, percent change, and percent add/subtract in one.

Math

Hong Kong service charge, extra tipping and bill-splitting in one tool.

Lifestyle

Estimate monthly bill using the latest CLP / HKE tariff.

Lifestyle

Enter each course grade and credit, get GPA on the 4.3 scale (HKU / CityU / HKUST / PolyU) or US 4.0 scale.

Education

Convert between Celsius (°C), Fahrenheit (°F) and Kelvin (K) instantly.

Conversion

Project the future value of a principal plus regular monthly or yearly contributions at a given annual rate, with total interest earned.

Finance

Estimate body fat percentage using the US Navy circumference formula (neck, waist, plus hip for women).

Health

Pick core and elective grades to see Best 5, 4C+1X and 4C+2X — the three weighting formulas used by JUPAS programmes.

Education

Pick your local and target cities to convert a given clock time across time zones.

Date & Time

Enter 2–6 positive integers to get the greatest common divisor (HCF / GCD) and least common multiple (LCM), with the Euclidean step chain shown.

Math

Enter a list of numbers to get the mean, median, mode, range plus standard deviation, variance and total.

Math

Estimate the fuel cost of a trip from distance, vehicle consumption and fuel price (one-way or round-trip).

Lifestyle

Enter the bill, service charge, tip and party size to get each person’s share — then round each share up to the nearest $1 / $5 / $10 / $20 / $50 to make cash collection painless.

Lifestyle

Given your current course grade and the weight of the final exam, find the exam score you need to hit a target overall grade.

Education

Enter the original price and a percent off (or fixed amount off) to see the final price, money saved and effective discount.

Lifestyle

Suggest ideal bedtimes or wake times based on 90-minute sleep cycles, so you wake up between cycles instead of mid-deep-sleep.

Health

Compute the compound annual growth rate from a start value, end value and number of years — useful for comparing long-term growth.

Finance

Enter your foot length or a size in any system to see the equivalent US / UK / EU and centimetre sizes.

Conversion

Estimate daily water intake from body weight, exercise duration and climate so you stay hydrated without overdoing it.

Health

Compute total profit, ROI % and annualised return from initial cost, final value and holding period — useful for comparing investments.

Finance

Enter the coefficients of ax² + bx + c = 0 to find the real or complex roots, discriminant and vertex.

Math

Add or subtract years, months, weeks and days from a start date to get the resulting date and weekday.

Date & Time

Estimate a password's bit entropy, brute-force time and strength tier. All computation happens in your browser.

Math

Pick a paper size (A0–A10, B / C series, Letter, Legal, card sizes) to see its mm / cm / inch / pixel dimensions.

Conversion

Convert between standard decimal numbers and scientific notation, with significant figures and order of magnitude.

Math

Estimate how long a piece of text takes to read from word count and words-per-minute, with presets for silent reading, reading aloud, proofreading and audiobook narration.

Education

Count the working days between two dates (excluding weekends) — or add N business days to a start date to find the deadline.

Date & Time

Convert between cups, tablespoons, teaspoons, millilitres, ounces and grams — for following overseas recipes or halving / doubling portions.

Lifestyle

Project the future purchasing power of an amount given an annual inflation rate and time horizon — and the nominal amount needed to keep up.

Finance

Convert a number simultaneously between binary, octal, decimal and hexadecimal — useful for programmers, students and electronics work.

Conversion

Compute pace per km / per mile from distance and time, or project finish time from a target pace — covers 5K, 10K, half- and full-marathon distances.

Health

Enter correct answers and total questions to get the percentage and letter grade — supports US A–F, US plus/minus, and UK honours (1st / 2:1 / 2:2 / 3rd).

Education

Convert between cost, selling price, markup % and gross margin % — handy for retail pricing and SMB profit analysis.

Finance

Compute 5 training heart rate zones from age and optional resting HR using the Karvonen formula (Z1 warm-up to Z5 max effort).

Health

Estimate the due date from your last menstrual period (LMP) using Naegele's rule, plus current gestational week, trimester and key pregnancy milestones.

Date & Time

Compute permutations P(n,r), combinations C(n,r) and factorial n! — useful for probability problems, lottery odds and combinatorics homework.

Math

Enter any two of voltage, current, resistance, or power — the calculator solves for the other two using V = IR and P = VI.

Science

Estimate lean body mass (LBM), fat mass and body fat % from height, weight and sex using the Boer, Hume and James formulas.

Health

Paste a list of numbers to compute mean, median, sample and population variance and standard deviation — with the working shown.

Math

Solve a triangle from 3 sides, 2 sides + 1 angle, or 2 angles + 1 side — area, perimeter and remaining parts via the law of sines / cosines.

Math

Enter any two of distance, time and speed to get the third — with km/h, mph, m/s, km, miles, hours and minutes supported.

Science

Compute density from mass and volume (ρ = m / V), or solve for the missing variable. Built-in reference table for 19 common substances.

Science

Enter launch speed, angle and height to compute projectile range, peak height and flight time (no air resistance). Pick from Earth, Moon, Mars and more.

Science

Split a daily calorie target into grams of carbs, protein and fat at any macro ratio.

Health

From an aspect ratio and one side, find the other; or from a diagonal and ratio, get real width and height (4:3, 16:9, 21:9 …).

Conversion

Compute the wind chill (feels-like temperature) from air temperature and wind speed using the 2001 Environment Canada / US NWS formula, with frostbite risk levels.

Science

Compute dew point from air temperature and relative humidity using the Magnus formula — handy for HVAC, photography and weather analysis.

Science

Compute kinetic energy KE = ½ m v² with mixed units (kg / g / lb and m/s / km/h / mph) and see the result in joules, kilojoules, food calories, foot-pounds and watt-hours.

Science

Given any two sides of a right triangle (two legs, or one leg plus the hypotenuse), instantly find the third side, area, perimeter and the two non-right angles.

Math

Enter any one of radius, diameter, circumference or area to get the other three — useful for design, engineering and DIY.

Math

Enter clock-in/clock-out times and break minutes to get total hours worked and gross pay — overnight (graveyard) shifts handled automatically.

Date & Time

Enter any three of initial amount, remaining amount, elapsed time and half-life to solve for the fourth — useful for radioactive decay, drug pharmacokinetics and radiometric dating.

Science

Compare two products by price-per-unit (per g, kg, ml, L or each). Enter price + amount + unit for each — see which is cheaper and by how much.

Lifestyle

Convert between bytes, KB, MB, GB, TB and PB — distinguishing decimal (1000-base, drive labels) from binary (1024-base, OS-reported).

Conversion

Convert between HEX (#RRGGBB), RGB(0–255) and HSL(0–360, 0–100, 0–100) instantly — with a live colour preview swatch.

Conversion

Estimate one-rep max from a sub-maximal lift (weight × reps) with Epley, Brzycki, Lombardi and Lander formulas, plus a 50–95% intensity training table.

Health

From fixed costs, variable cost per unit and selling price, find the units needed to cover all costs — plus break-even revenue, contribution margin, target-profit volume and margin of safety.

Finance

Enter a percentage (or score out of total) and map it to a letter grade and GPA across four standard scales — US 4.0 with +/−, US 10-point, UK Honours, and IB 1–7.

Education

Convert hourly wage to monthly / annual salary or back — with customisable hours per week and weeks worked per year. Works for part-time, freelance and salaried jobs.

Lifestyle

Pick any date to see which day of the year (1–366), ISO 8601 week number, weekday, and how many days from the start and end of the year.

Date & Time

Estimate body surface area from height and weight using the Mosteller, Du Bois, Haycock and Boyd formulas — commonly used in drug-dosing, chemotherapy and cardiac-index calculations.

Health

Two-way conversion between Arabic numbers (1–3999) and Roman numerals (I, V, X, L, C, D, M) — handy for typesetting, chapter titles and homework.

Math

Pick the colour bands and instantly read the resistance and tolerance — 4-band and 5-band notations supported, with Ω / kΩ / MΩ formatting and a closest E12 / E24 preferred-value check.

Science

Enter two latitude/longitude pairs to compute the great-circle distance using the haversine formula (km, miles, nautical miles), with bearing and midpoint.

Science

Convert a P-metric tire spec (e.g. 225/65R17) into sidewall height, overall diameter, circumference and revolutions per km — and compare against a reference size to see speedometer error.

Conversion

Convert a nominal annual rate (APR) at any compounding frequency to the effective annual yield (APY), or solve the inverse — essential for comparing credit-card, savings-account and mortgage rates.

Finance

Translate a class or cohort rank into percentile rank using all three common conventions (CDF, mid-rank, inclusive) plus quartile / decile / top-X% labels — for college applications, scholarships and standardized-test comparisons.

Education

Convert between joules, kilojoules, calories, kilocalories, kilowatt-hours, BTU and watt-hours in a single view — for nutrition labels, electricity bills, heating and fuel comparisons.

Conversion

Quickly estimate how many years to double your money at a given compound rate, or what rate is needed to double in a target period — with the exact logarithmic answer alongside.

Finance

Enter any Gregorian date (past or future) to instantly find the day of the week — useful for birthdays, anniversaries and historical events.

Date & Time

Estimate a dog's human-equivalent age from its actual age and size (small / medium / large / giant), with both the classic "×7" rule and modern research curves side by side.

Lifestyle

Solve any one of C₁, V₁, C₂, V₂ from the dilution equation C₁V₁ = C₂V₂ — a daily lab essential for chemistry, biology and pharmacy work.

Science

Enter two points (x₁, y₁) and (x₂, y₂) to instantly get the slope, y-intercept, line equation y = mx + b, distance, and midpoint — a classroom staple for algebra and coordinate geometry.

Math

Enter group size n to see the probability that at least two people share a birthday — the classic birthday problem.

Math

From balance, monthly payment and APR, compute how many months until the loan is paid off, the total interest paid, and the minimum payment that just covers interest.

Finance

Given goal amount, current savings, monthly deposit and APR, see how many months it takes to hit the target.

Finance

Two 80 dB sound sources do not equal 160 dB. Enter multiple dB values to compute the combined SPL, and subtract background noise to recover the signal alone.

Science

Enter classes attended, classes missed and total classes in the term to see your current attendance %, the maximum classes you can still skip, or how many you must attend to reach your target (default 75 %).

Education

Compute logₐ(x) for any base — natural log (ln), common log (log₁₀), binary log (log₂) and a custom base, with the change-of-base steps shown.

Math

Enter up to 8 resistor values to see the series total (R₁ + R₂ + …) and the parallel total (1 / Σ(1/Rᵢ)) at the same time.

Science

Convert between electromagnetic wavelength and frequency via c = λf, with the matching spectrum band (radio / microwave / visible / X-ray / γ) and photon energy.

Science

How many people, how hungry, and how many slices per pizza? Get the exact number of pizzas to order — no leftovers, no shortages.

Lifestyle

Convert a Unix timestamp (seconds or milliseconds since 1970-01-01 UTC) to UTC, Hong Kong time and RFC 1123 HTTP date — and back. Built for debugging log files, API responses and database fields.

Date & Time

Enter room dimensions and tile size to estimate the number of tiles needed (including a configurable waste allowance) — for floor or wall jobs.

Lifestyle

Project a finish time at one distance from a known time at another distance using the classic Riegel formula T₂ = T₁ × (D₂/D₁)^1.06.

Health

Compute the capacity of vertical or horizontal cylindrical, rectangular and spherical tanks, including partial-fill volumes at a given liquid level.

Science

Paste text to instantly count words, characters (with and without spaces), sentences, paragraphs, average word length and estimated reading time.

Education

Enter a value, the mean and the standard deviation to compute the z-score and the corresponding normal-distribution percentile and probabilities.

Math

Convert between Pa, kPa, bar, mbar, atm, psi, mmHg, Torr and inHg in a single view — all the everyday pressure units.

Conversion

From room length, width and height, door and window area, paint coverage per litre and the number of coats, estimate how many litres of paint you need.

Lifestyle

Compute mean arterial pressure from systolic and diastolic blood pressure with clinical bands and pulse-pressure context: MAP = DBP + (SBP − DBP)/3.

Health

Compute cumulative smoking exposure in pack-years from cigarettes per day and years smoked, with lung-cancer-screening thresholds.

Health

Divide waist by hip circumference and check the WHO risk bands — a quick screen for central obesity and cardiovascular risk.

Health

Enter the screen resolution and diagonal size to get pixel density (PPI), real width/height, dot pitch and total pixel count.

Math

Pick a year and the Computus algorithm returns Easter Sunday plus Ash Wednesday, Palm Sunday and Good Friday.

Date & Time

Paste an English passage and instantly get the Flesch Reading Ease and Flesch-Kincaid Grade Level scores — the standard readability metrics used by US schools, MS Word and government plain-language guidelines.

Education

Enter the pendulum length and local gravity to get the period, frequency and angular frequency, with Earth/Moon/Mars/Jupiter presets — and reverse-solve for the length needed to hit a target period.

Science

Pick a brew method (pour-over, French press, cold brew or espresso) and a desired output, and get the exact coffee dose and water weight to match the recommended ratio.

Lifestyle

Convert between N·m, kgf·m, kgf·cm, lbf·ft, lbf·in and ozf·in — all the torque units used on torque wrenches, bicycle bolts and car service specs.

Conversion

Convert between degrees, radians, gradians, turns, arcminutes, arcseconds, milliradians and NATO mil — with live sin/cos/tan values for reference.

Conversion

Convert between L/100km, km/L, US MPG and UK (imperial) MPG — compare car efficiency figures across regions without arithmetic.

Conversion

Enter principal, annual rate and number of periods to compute the fixed annuity payment (PMT formula) — essential for retirement-income planning.

Finance

Enter the number of tickets / selections and see the actual probability of hitting first, second … prizes in a Mark Six (6-of-49) draw.

Math

Enter any date to compute the lunar phase (new, first quarter, full, last quarter …), moon age in days and illuminated fraction.

Date & Time

Enter the room size, roll dimensions and pattern repeat to get the number of wallpaper rolls to order (with pattern-match waste included).

Lifestyle

Enter air temperature and relative humidity to get the apparent temperature (NOAA Rothfusz heat index) and the corresponding heat-stress risk band.

Science

Enter the after-tax salary you want to take home and the calculator works back to the gross figure you need to offer (HK MPF and salaries-tax aware).

Finance

Convert between W, kW, MW, mechanical horsepower (hp), metric horsepower (PS), BTU/hr, ft·lbf/s, cal/s, kcal/h and refrigeration tons in one view.

Conversion

Convert any decimal (including repeating decimals) to a simplified fraction and a mixed number.

Math

Enter speed, reaction time and road friction to estimate reaction, braking and total stopping distance.

Science

Use METs, body weight and duration to estimate calories burned for common activities (running, hiking, swimming, cycling and more).

Health

Enter your Listening, Reading, Writing and Speaking scores to get the IELTS overall band using the official rounding rule (.25 rounds up to .5, .75 rounds up to the next whole band).

Education

Give a sphere any one of radius, diameter, surface area or volume and instantly get the other three — plus the great-circle circumference and area.

Math

Enter the radius and height of a cylinder to get volume (π r²h), lateral surface, base area and total surface area.

Math

Enter the refractive indices of two media and an angle of incidence — get the refraction angle and critical angle from Snell's law (n₁ sin θ₁ = n₂ sin θ₂).

Science

Estimate how many pages a piece of writing will fill from word count, font size and line spacing.

Education

Find your Chinese zodiac animal, stem-branch element, zodiac year and lunar (nominal) age from any birth date.

Date & Time

Enter cigarettes per day, price per pack and years smoked — see your total spend and how much you could save by quitting.

Lifestyle

Compute nPr — the number of ordered arrangements of r items chosen from n — alongside n!, r! and the related combination nCr.

Math

Enter your birth date to see your Western zodiac sign (Aries, Taurus, Gemini…) along with its element, modality and opposing sign.

Date & Time

Pick a birth month to instantly see the modern and traditional birthstones, the birth flower, the spanning zodiac signs and a colour swatch — handy when choosing jewellery or birthday gifts.

Date & Time

Enter your six IB subject grades (HL/SL) plus the EE/TOK bonus matrix to compute your total IB Diploma score out of 45.

Education

Enter A-Level, AS, EPQ, IB or BTEC grades to compute your total UCAS Tariff points and see how they line up against AAA / AAB / ABB conditional offers.

Education

Enter an SAT total or ACT composite score and instantly see the equivalent score range using the official 2018 College Board / ACT concordance table.

Education

Factor any integer from 2 up to 10¹² into primes, see the canonical exponent form, count and list all divisors.

Math

Convert a Gregorian calendar date to its Julian Day Number (JDN) and Modified Julian Day (MJD) — used in astronomy, history, and cross-calendar date math.

Date & Time

Enter property price, monthly rent and yearly expenses (rates, management, insurance, vacancy) to see both gross and net rental yield (%).

Finance

Convert any roof rise / run into the X-in-12 pitch notation used by builders, plus the slope angle in degrees, slope percentage and the rafter-length multiplier.

Lifestyle

Enter slab length, width and thickness with a waste factor and get the concrete volume (m³, yd³, ft³) plus the approximate number of 25 kg, 40 kg or 80 lb pre-mix bags required.

Lifestyle

Pick the dose (mg) and the time you drank it; the calculator uses the standard ~5-hour caffeine half-life to project how many milligrams remain hour-by-hour, including the level at bedtime.

Health

Pick a root font-size (defaults to 16 px) and convert any CSS pixel, rem, em, percentage or point value into the others, with a reference table for common sizes.

Conversion

Enter capacitance (F, mF, µF, nF, pF) and voltage to compute the stored energy (E = ½CV²) and charge (Q = CV) on a capacitor.

Science

Enter total rise and a target riser height to get the number of risers, actual riser height, tread depth, stringer length, pitch and a side-by-side compliance check against the IRC, IBC and UK Approved Document K.

Lifestyle

Bergman’s BAI estimates body-fat percentage from hip circumference and height alone (BAI = hip ÷ height^1.5 − 18) — no scale required.

Health

Enter any date and compute its ISO 8601 week number, ISO year and weekday — using the Monday-first / first-week-contains-Jan-4 rule.

Date & Time

Enter annual dividend per share, share price, EPS and amount invested to compute dividend yield (%), payout ratio (%) and projected yearly income.

Finance

Convert alcohol by volume (ABV %) to US proof and UK proof, plus compute grams of pure alcohol and "standard drinks" per pour for US / UK / AU / HK.

Conversion

Convert network bandwidth (kbps, Mbps, Gbps) to file-transfer rate (KB/s, MB/s, MiB/s) and estimate how long a given file size takes.

Conversion

Enter an IELTS, TOEFL iBT, Cambridge English Scale or TOEIC score and instantly map it to a CEFR level (A1 – C2).

Education

Enter a price and a tax rate to compute the gross total and tax amount, or work backwards from a tax-inclusive price to the net amount.

Finance

Enter age, sex, height and weight to compare all five activity levels side-by-side — instantly see the daily calories you need to maintain weight.

Health

Kilograms, grams, milligrams, pounds, ounces, stones, tonnes, jin and tael — common mass units, converted instantly.

Conversion

Enter room area, ceiling height, sun exposure, occupants and climate to find the recommended air-conditioner BTU rating / horsepower.

Lifestyle

Enter property value and loan amount to get the LTV ratio, the required down-payment, and a live check against HKMA caps and the HKMC mortgage insurance ceilings.

Finance

Enter battery capacity (mAh) and voltage (V) to get watt-hours (Wh) instantly — with a live IATA airline check (100 Wh / 160 Wh cut-offs).

Conversion

Enter altitude to compute the boiling point of water (°C / °F) and local air pressure using the ICAO standard atmosphere and the Antoine equation — useful for hiking, cooking and high-altitude baking.

Science

Combine your current cumulative GPA and total credits with this term’s GPA and credits to see the updated cumulative GPA and how much it moved.

Education

Discount a future amount back to today using an annual rate, horizon and compounding frequency — get the present value, discount factor and effective annual rate.

Finance

Use the Fisher equation to strip inflation from a nominal rate and find the real return, with the common r ≈ i − π approximation alongside.

Finance

Compute the n-th root of the product of n positive numbers — the right average for growth rates, returns and ratios — alongside the arithmetic mean for comparison.

Math

Enter two clock times (HH:MM[:SS]) and instantly see the difference in hours, minutes and seconds — with overnight-shift handling and decimal-hour output.

Date & Time

Enter any integer n from 0 to 1500 to instantly compute F(n) and F(n−1) with BigInt precision, the consecutive-term ratio (converging to the golden ratio φ) and the first 30 terms of the sequence.

Math

Convert between TOEFL iBT total scores (0-120) and IELTS Academic Band scores (4.5-9.0) using the official 2018 ETS concordance.

Education

Enter underbust and bust (or pick a local size) to convert bra sizes across US, UK, EU, AU and JP standards.

Conversion

Enter years of service and see the statutory paid annual leave entitlement under the HK Employment Ordinance §41AA.

Date & Time

Convert numbers into English words and Chinese cheque-style capital form (壹貳參…) for writing cheques, contracts or homework.

Education

Enter inner circumference (mm) or diameter to cross-reference US, UK, EU, JP and HK ring sizes.

Conversion

Enter your wedding date to see the anniversary number, days until the next one, and the traditional / modern gift theme (paper, silver, gold…).

Lifestyle

Estimate blood alcohol concentration (BAC %) with the Widmark formula from drinks consumed, body weight, sex and hours elapsed — and compare against the Hong Kong 0.05% drink-driving limit.

Health

Solve Q = m × c × ΔT for any one of heat energy, mass, specific heat capacity or temperature change — with presets for water, aluminium, iron, copper, glass, air and more.

Science

Convert between pH, pOH, hydrogen-ion concentration [H⁺] and hydroxide concentration [OH⁻] — with acid / neutral / alkaline classification.

Science

Pick the unknown (P, V, n or T), enter the other three and PV = nRT is solved instantly — works in Pa / kPa / atm / bar / mmHg / psi, m³ / L / mL, mol / mmol / kmol and K / °C / °F.

Science

Enter your distance covered in a 12-minute run to estimate VO₂ max and read off the age/sex fitness category.

Health

Convert oven temperatures between Celsius, Fahrenheit and British gas marks, with descriptive labels (slow / moderate / hot / very hot).

Lifestyle

Enter the total focus time you want and get the required 25-minute Pomodoro count, short/long break tally and overall wall-clock duration.

Education

Enter your date of birth to see when your next half-birthday falls, how many days away it is, and your current half-age (e.g. 33.5 years).

Date & Time

Enter a latitude, longitude and date to get the local sunrise, sunset, solar noon and total daylight hours using the NOAA solar position formula.

Date & Time

Apply the Trinity Study 4% rule: enter your retirement nest egg and a withdrawal rate to see the annual and monthly income it can support.

Finance

Enter monthly debt payments and gross monthly income to compute your DTI ratio against the standard lender bands (36% / 43% / 50%).

Finance

Enter a study date and ease factor and use the SuperMemo SM-2 algorithm to project the next review dates — handy for flashcards or vocabulary.

Education

Square metres, hectares, acres, square feet, square miles and more — common area units, converted instantly.

Conversion

Litres, millilitres, cubic metres, US and imperial gallons, quarts, pints, fluid ounces, cups, tablespoons and teaspoons — converted instantly.

Conversion

Convert freely between km/h, mph, m/s, ft/s, knots and Mach number.

Conversion

Enter principal, annual rate and term and apply I = P × r × t to find the interest earned or owed under simple-interest accrual (no compounding).

Finance

Enter two point charges and the separation distance to compute the electrostatic force between them via F = kₑ·q₁·q₂/r² (attractive or repulsive).

Science

Enter two masses and the distance between them to compute the gravitational attraction via F = G·m₁·m₂/r².

Science

Given any two of the three quantities (object distance u, image distance v, focal length f), solve for the remaining one and the lateral magnification.

Science

Enter the initial outlay, future cash flows and a discount rate to compute the project Net Present Value (NPV) — positive NPV means the project beats your required return.

Finance

Pick the number of dice, sides (d4 / d6 / d8 / d10 / d12 / d20) and a target sum to compute the probability of rolling exactly that total, at least, or at most.

Math

Enter the observer eye height above the surface to compute the distance to the geometric and refraction-corrected horizon.

Science

Given any two of spring constant k, displacement x or restoring force F, solve for the third and the elastic potential energy U = ½kx².

Science

Enter the upfront investment, projected yearly cash flows and a hurdle rate to solve for the discount rate that makes NPV = 0 — and see at a glance whether the project beats your required return.

Finance

Enter fluid density, submerged volume and gravitational acceleration to compute the buoyant force F = ρ V g, plus whether the object floats, sinks or stays neutral.

Science

Enter first term a, common difference d and number of terms n to compute the nth term aₙ and the partial sum Sₙ = n/2·(2a + (n − 1)d).

Math

Enter your bodyweight and training goal to get a science-backed daily protein range (g/day) and per-meal split, based on RDA, ISSN and ACSM/AND/DC guidelines.

Health

Enter a target date and get an instant breakdown of days, weeks, months, hours and minutes remaining — or elapsed for past dates.

Date & Time

Enter original servings and desired servings to scale every ingredient proportionally, with friendly rounding to common cookware-sized amounts.

Lifestyle

Enter your last menstrual period (LMP) date and average cycle length to estimate the next ovulation day, fertile window and next period.

Health

Enter your cat's real age to estimate the human-equivalent age using the standard veterinary formula and see the matching life stage (kitten, adult, senior, geriatric).

Lifestyle

Estimate total body water (in litres) and the percentage of body weight using the Watson formula based on age, sex, height and weight.

Health

Enter foreground and background hex colors to compute the WCAG 2.x contrast ratio (1:1 to 21:1) and see whether the pair passes AA / AAA accessibility levels for normal and large text.

Conversion

Enter the number of time zones crossed and direction of travel (eastward or westward) to estimate how many days you typically need to fully adjust to the destination, based on sleep-medicine rules of thumb.

Date & Time

Enter the input voltage and two series resistor values to find the divider output voltage, current and power dissipated in each resistor.

Science

Enter confidence level, margin of error, expected proportion (and optional population size) to compute the survey sample size you need.

Math

Enter your portfolio annual return, the risk-free rate and the annualised standard deviation to compute the Sharpe ratio — excess return earned per unit of risk taken.

Finance

Enter the first term a, common ratio r and number of terms n to find the sum of the first n terms of a geometric series — plus the infinite-series sum when |r| < 1.

Math

Convert between HH:MM:SS and decimal hours both ways — built for payroll, timesheets and lab notebooks.

Date & Time

Enter base radius and height to get the cone volume, slant height, lateral, base and total surface area.

Math

Enter price, expected number of uses and upkeep cost to compute true cost per use — see whether that item is really worth it.

Lifestyle

Compare your current mortgage against a new rate, net of refinance closing costs and penalties, to find how many months to break even and whether the whole loan saves or costs more over its lifetime.

Finance

Enter characters typed, elapsed time and errors to get gross WPM, net WPM and accuracy — the standard typing-test metrics used worldwide.

Education

Enter step count, height (auto-derives stride length) and body weight to estimate distance walked (km / mi), stride length, calories burned and your daily activity tier.

Health

From face value, coupon rate, yield-to-maturity, years to maturity and coupon frequency, compute a fixed-coupon bond's present price, premium/discount and current yield.

Finance

Enter the mass and radius of a celestial body (or pick Earth, Moon, Mars and other presets) to compute the minimum surface launch speed v = √(2GM/r) needed to escape its gravity.

Science

Paste your paper citation counts to instantly compute the h-index, g-index, i10-index and other bibliometrics used to quantify a researcher's scholarly impact.

Education

Enter a food's glycemic index (GI) and grams of carbs per serving to compute glycemic load GL = GI × carbs ÷ 100 — a better predictor of real blood-sugar response than GI alone.

Health

Estimate hiking time with the classic Naismith's Rule (1 h per 5 km plus 1 h per 600 m of ascent), with optional descent and rest-time corrections.

Lifestyle

Enter the source frequency, observer/source velocities and wave speed (sound or light) to compute the observed frequency shift due to the Doppler effect.

Science

Convert HbA1c (%) to estimated average glucose (eAG) in both mg/dL and mmol/L — and back again — to help diabetes and prediabetes patients read their lab reports.

Health

Enter power (W / kW / hp) and weight (kg / lb) to instantly compute W/kg, hp/kg and hp/lb ratios with cyclist and car performance bands.

Lifestyle

Enter the total exam time, number of questions and optional review reserve to get the average time per question and 25/50/75 % pacing checkpoints — ideal for SAT, GRE, HKDSE and similar timed exams.

Education

Enter initial temperature, ambient temperature, cooling constant and elapsed time to estimate an object's temperature with T(t) = T∞ + (T₀ − T∞)·e^(−kt), plus half-cooling time and time constant.

Science

Enter a birth year to classify yourself by the Pew Research generation cohorts — Greatest, Silent, Boomer, Gen X, Millennial, Gen Z, Gen Alpha or Gen Beta.

Date & Time

Enter current accumulated practice hours and weekly hours available to project when you will hit the 1,000 / 5,000 / 10,000-hour mastery milestones popularised by Ericsson and Gladwell.

Education

Enter mass and radius, then linear speed, angular speed or period, and instantly read off centripetal force F = m·v²/r, centripetal acceleration, tangential speed, angular speed, period and frequency.

Science

Look up the diameter (mm), cross-sectional area (mm²), resistance per kilometre and safe ampacity for any American Wire Gauge (AWG) size — handy for low-voltage wiring design.

Conversion

Enter inductance L (H) and capacitance C (F) to compute the resonant frequency f = 1 / (2π√(LC)) of an LC tank circuit, plus its period and angular frequency.

Science

Enter the air temperature and compute the speed of sound in dry air using v = 331.3 × √(1 + T/273.15) — output in m/s, km/h, mph, ft/s plus the "count-the-seconds" thunder distance rule.

Science

Enter battery capacity (kWh), charger power (kW) and the start / target state of charge to estimate how long an EV charging session takes, with adjustments for charging efficiency and the constant-current → constant-voltage taper above 80 %.

Lifestyle

Enter the original gravity (OG) and final gravity (FG) of a beer or wine ferment and the calculator returns the standard homebrewing ABV estimate ABV ≈ (OG − FG) × 131.25, plus apparent attenuation and a calorie estimate.

Lifestyle

Pick a note (C, C♯, D, …), octave and tuning reference A4 (440 Hz by default) and the tool returns the frequency in Hz, the wavelength in air and the MIDI note number via f = A4 × 2^((n − 69)/12).

Math

Enter height, weight and body-fat percentage to compute Fat-Free Mass Index (FFMI) and the height-adjusted FFMI used to gauge muscularity.

Health

Enter fluid density, velocity, characteristic length and viscosity to compute the Reynolds number and classify the flow as laminar, transitional or turbulent.

Science

Enter the spring constant k and displacement x to instantly compute the elastic potential energy stored in a Hookean spring via U = ½·k·x², with conversions to kJ, kcal, ft·lbf and Wh for easy comparison.

Science

Enter two known points (x₁, y₁) and (x₂, y₂) and a target x to instantly read off y via y = y₁ + (x − x₁)(y₂ − y₁)/(x₂ − x₁) — the tool flags whether your x sits inside the two points (interpolation) or outside (extrapolation).

Math

Use A = ε·c·ℓ to compute absorbance, transmittance and concentration — any three of the four inputs determines the fourth.

Science

Add or subtract any number of HH:MM:SS durations with automatic carry — handy for totalling video lengths, training sessions or race splits.

Date & Time

Enter the two parallel sides and height of a trapezoid to get its area, midsegment length and perimeter when the legs are known.

Math

Compute the future value of a stream of equal payments (e.g. monthly savings or pension contributions) with end- or beginning-of-period timing.

Finance

Convert between Hz, kHz, MHz, GHz, THz, RPM and BPM — one input fills every other unit instantly.

Conversion

Convert between newtons (N), kilonewtons (kN), pound-force (lbf), kilogram-force (kgf), dyne and ounce-force (ozf) — bridging SI, imperial and CGS force units used in physics and engineering.

Conversion

Convert magnetic flux density between tesla (T), millitesla (mT), microtesla (µT), gauss (G) and milligauss (mG) — handy for comparing MRI fields, Earth field, speakers and lab magnets across very different scales.

Conversion

Pick any date to see what percentage of the year, quarter, month and week has elapsed and how many days remain — handy for yearly goals, OKR check-ins and progress reports.

Date & Time

Compute orbital period from semi-major axis and central body mass via T² = 4π²·a³/GM, or invert to recover the semi-major axis — with presets for the Sun, Earth, Moon and Jupiter.

Science

Enter the number of trials n, the per-trial success probability p and a target number of successes k to get P(X = k), P(X ≤ k), P(X ≥ k) along with the distribution mean and standard deviation.

Math

Paste two parallel data series (X and Y) and get the Pearson correlation coefficient r, r², the best-fit line slope and intercept, and the sample means and standard deviations.

Math

Enter fluid density, velocity, drag coefficient Cd and frontal area and compute the drag force from Fd = ½·ρ·v²·Cd·A — handy for cycling, automotive, ballistic and skydiving scenarios.

Science

Compute the hydrostatic pressure P = ρ·g·h from fluid density, depth and gravity, and convert it to kPa, bar, psi, atm, mmHg and metres of water — useful for diving, aquariums and piping.

Science

Enter the market values of equity and debt, the cost of equity, the cost of debt and the corporate tax rate to compute the weighted-average cost of capital (WACC), capital-structure weights and after-tax cost of debt.

Finance

Enter the sample mean, sample standard deviation, sample size and confidence level to compute a confidence interval for the population mean using the t (or z) distribution, with margin of error and standard error.

Math

Enter pKa together with the conjugate-base [A⁻] and weak-acid [HA] concentrations and apply the Henderson–Hasselbalch equation to compute buffer pH, the buffer ratio and the effective buffering range.

Science

Enter mass, incline angle and friction coefficients (or pick a preset like steel-on-steel or rubber-on-concrete) to compute normal force N, maximum static friction fs,max = μs·N, kinetic friction fk = μk·N and the critical angle θc — and instantly see whether the block stays at rest or slides down the slope.

Science

Enter height and sex to compare the four classic ideal-body-weight formulas (Devine, Robinson, Miller, Hamwi), with their average and a ±10 % healthy-weight band.

Health

Enter the means, standard deviations and sample sizes of two groups to compute Cohen's d and Hedges' g effect sizes, classified per Cohen 1988 as trivial / small / medium / large.

Math

Enter the area and target depth to compute the volume of mulch, soil or gravel needed (in litres, m³ and cubic yards), and estimate bag count and total cost.

Lifestyle

Enter a company's net income, preferred dividends and weighted-average common shares outstanding to compute basic EPS, with an optional dilutive-securities input for diluted EPS.

Finance

Enter multiple assignments (homework, quizzes, mid-term, project, final) with their scores and weights to compute the weighted-average overall grade, plus the points already locked in and the weight still to come.

Education

Enter dividend a and divisor n to compute the quotient and remainder a mod n. The truncated (C / JavaScript %), floored (Python / mathematical) and Euclidean conventions are shown side by side so the negative-input differences are obvious.

Math

Enter the dimensions of your tank — rectangular, cylindrical or bow-front — to get the water volume in litres, US gallons, UK gallons and water weight, with a fill-percentage adjustment for substrate and décor.

Lifestyle

Enter the memory strength S and elapsed time t to compute the retention rate per Ebbinghaus R = e^(−t/S), with a suggested next-review time (when retention drops to 80–90 %).

Education

Enter raw class scores to compute each student's z-score, percentile and curved A–F letter grade using the classic ±0.5σ / ±1.5σ cut-offs, along with the resulting grade distribution.

Education

Pick a date and see it instantly formatted in ISO 8601, RFC 2822, US (MM/DD/YYYY), EU (DD/MM/YYYY), Japanese (YYYY年MM月DD日), Unix timestamp and a dozen other common formats.

Date & Time

Select 0–2 points for each of the five APGAR signs (Appearance / Pulse / Grimace / Activity / Respiration) to get the total APGAR score (0–10) and clinical band (normal / moderately depressed / severely depressed).

Health

Pick eye-opening (1–4), verbal (1–5) and motor (1–6) responses to compute the Glasgow Coma Scale total (3–15) with mild / moderate / severe banding.

Health

Enter driving and driven gear tooth counts plus input RPM and torque to compute gear ratio, output RPM, output torque and mechanical advantage.

Science

Enter solute mass, molecular weight and solution volume to compute molarity (mol/L); solve for any one unknown.

Science

Toggle read/write/execute for user, group and other to instantly get both octal (e.g. 755) and symbolic (e.g. rwxr-xr-x) notations.

Math

Enter 2D or 3D vector components (x, y, z) to compute the magnitude, unit vector and direction angles.

Math

Convert moment magnitude (Mw) to released energy (joules and TNT equivalent) via the Gutenberg–Richter relation log₁₀E = 1.5M + 4.8, with a comparison to landmark historical earthquakes.

Science

Enter a fixed amount per period and the buy price for each period to see total invested, total shares, average cost and current value — with a side-by-side comparison against putting the same money in as a lump sum at the first price.

Finance

Enter your word count and speaking pace to estimate how long a speech, presentation, sermon or classroom talk will take, including pause time.

Education

List every Friday the 13th in a given year (or range) and show how many days remain until the next one.

Date & Time

Enter account size, per-trade risk percent and stop-loss distance to compute the share/lot quantity that caps your loss at the chosen risk.

Finance

Enter flour weight and target hydration to get water, salt and yeast quantities via baker's percentage — with Neapolitan, NY and Sicilian style presets.

Lifestyle

Enter parcel length × width × height and DIM divisor (IATA air 6000 cm³/kg, express 5000, UPS/FedEx US 139 in³/lb) to compute volumetric weight and compare it with actual weight to find the chargeable weight.

Conversion

Enter experimental and theoretical (accepted) values to get absolute percent error, signed relative error, and absolute error. Switch to percent-difference mode to compare two measurements where neither is the accepted value.

Math

Enter the actual mass of product recovered and the theoretical yield to compute % yield = actual ÷ theoretical × 100%, with an indicative classification (poor / moderate / good / excellent).

Science

Pick a common shape (solid sphere, hollow sphere, solid cylinder, thin-walled cylinder, thin disk, slender rod about centre or end, rectangular plate) and enter mass and dimensions to get the rotational moment of inertia I = k·m·r² / k·m·L².

Science

Enter air temperature, barometric pressure and relative humidity to compute air density (kg/m³) via the CIPM partial-pressure form and the Magnus-Tetens saturation vapour pressure — useful for cyclists, runners, pilots and aerodynamics estimates.

Science

Pick a month, year, weekday and occurrence (including "last") to get the date — handy for scheduling monthly meetings, paydays and rule-based holidays such as US Thanksgiving (4th Thursday of November).

Date & Time

Enter several debts (balance, APR, minimum payment) and your monthly extra budget; the tool runs the classic "smallest balance first" snowball method, estimating each debt's payoff month, total interest paid and total months to debt-free.

Finance

Enter a fall height (and optional mass / gravity) to compute fall time, impact velocity and kinetic energy via h = ½·g·t² and v = √(2·g·h). Preset gravities for Earth, Moon, Mars and more.

Science

Enter the mean event rate λ and an event count k to get P(X = k), P(X ≤ k), P(X ≥ k), the mean, variance and standard deviation — useful for queueing, call-centre staffing and rare-event modelling.

Math

Enter an initial investment, level annual cash inflow, discount rate and horizon to instantly see the simple payback period, the discounted payback period and the terminal Net Present Value (NPV), plus a year-by-year cumulative cash-flow table — built for capital-budgeting, small-business investments, solar installs and equipment purchase decisions.

Finance

Enter a chemical formula (e.g. H2SO4, Ca(OH)2, CuSO4·5H2O) and the tool sums the IUPAC standard atomic weights element by element to return the molar mass in g/mol — useful for chemistry homework and lab weighing.

Science

Enter the prior P(A), the sensitivity P(B|A) and the false-positive rate P(B|¬A); the tool applies Bayes’ theorem to give the posterior P(A|B) — handy for medical tests, spam filters and any classification decision.

Math

Enter a circle’s radius and central angle (degrees or radians) to compute the arc length s = r·θ, sector area A = ½·r²·θ and chord length — useful for geometry, machining and architectural layout.

Math

Enter your current salary, raise percentage or dollar amount and instantly see your new salary plus annual, monthly, weekly and hourly differences — handy for comparing offers, negotiating reviews and gauging inflation-adjusted raises.

Finance

Enter the entries of a 2×2 or 3×3 matrix and instantly get the determinant det(A) via ad − bc or cofactor expansion along the first row, with an invertibility check and the step-by-step 2×2 minors shown for linear-algebra study.

Math

Convert Cartesian (x, y) ↔ polar (r, θ) coordinates in either direction with a degree/radian toggle — useful for math, physics, engineering and game-development work.

Conversion

Enter a start and end date and instantly see how many Mondays, Tuesdays, … Sundays fall inside the range, plus weekday vs weekend totals — useful for scheduling, payroll, rent and contract counts.

Date & Time

Enter a target amount (FV), expected annual return and term — the tool back-solves the periodic payment you need to reach that target, the classic "how much to save monthly to hit $X by year Y" question.

Finance

Enter any two of force, mass and acceleration and the tool solves for the third — handy for high-school physics, machine design, vehicle braking and elevator safety factors.

Science

Enter two 2D or 3D vectors and instantly compute the dot product, included angle, scalar projection and vector projection — with hints for orthogonal, parallel and anti-parallel cases.

Math

Enter two numeric vectors of any dimension and compute cos θ = (a·b) / (|a|·|b|), plus the angular distance — the staple similarity metric in NLP, recommender systems and document-similarity scoring.

Math

Enter two values and compute the symmetric percent difference |a − b| / ((|a| + |b|) / 2) alongside the directional percent change (b − a)/a — a common source of confusion in lab reports and news headlines.

Math

Enter two 3D vectors a and b, compute the cross product a × b together with its magnitude (the area of the parallelogram they span) and sin θ — the workhorse of physics torque, computational geometry and 3D graphics.

Math

Enter two points in the plane or in 3D space and the tool returns the straight-line Euclidean distance √Σ(Δᵢ)², each axis delta and the midpoint — handy for geometry homework, CAD measurements and planar GIS work.

Math

Enter the level periodic cash flow C and the discount rate r — the tool returns the perpetuity present value PV = C / r and, optionally, the growing-perpetuity Gordon value PV = C / (r − g) used for consols, preferred shares and dividend-discount models.

Finance

Enter mass and molar mass (g/mol), or moles, and the tool converts via n = m / M, also reporting the particle count N = n · Nₐ — the everyday workhorse of chemistry lab weighing and stoichiometry problems.

Science

Enter a dataset and the tool returns the coefficient of variation CV = σ / μ × 100% (standard deviation divided by mean) — the standard yardstick for comparing dispersion across datasets with different units or magnitudes (lab repeatability, portfolio risk).

Math

Enter a dataset and the tool sorts it and returns the median, first and third quartiles, the inter-quartile range (IQR) and Tukey 1.5×IQR outlier fences — the five-number summary behind every box plot.

Math

Enter a set of positive numbers and compute the harmonic mean HM = n / Σ(1/xᵢ) alongside the arithmetic and geometric means — the right average when the data behaves like rates or denominators (speeds, P/E ratios, flow rates).

Math

Enter a list of class probabilities or frequencies and compute Shannon entropy H = −Σ pᵢ log₂ pᵢ (bits) alongside the maximum entropy and the normalised entropy — the foundation of information theory, decision-tree splits and password analysis.

Math

Enter an original price and two discounts applied in sequence (e.g. "30% off then an extra 10%") — the tool returns the final price, the equivalent single discount and the savings, sidestepping the common mistake of simply adding the percentages.

Lifestyle

Enter the side count n and side length s of a regular polygon and the tool returns the interior and exterior angles, the apothem and circumradius, the area and the perimeter in one shot — works for triangles, squares, pentagons, hexagons and beyond.

Math

Enter the loan amount, the number of discount points bought and the rate reduction per point — the tool returns the upfront cost, the monthly payment saving and the break-even month so you can decide whether paying points is worth it.

Finance

Enter a velocity v (as a fraction of c or in m/s) and compute the special-relativity Lorentz factor γ = 1/√(1 − v²/c²), together with the time-dilation factor, the length-contraction ratio and the relativistic kinetic energy.

Science

Enter surface area A, temperature T (kelvin) and emissivity ε, then compute the radiant power P = ε σ A T⁴ under the Stefan–Boltzmann law — the standard formula for thermal radiation, the solar constant and stellar luminosity estimates.

Science

Enter the moles (or mass + molar mass) of each component in a mixture and compute the mole fraction xᵢ = nᵢ / Σ nⱼ for every component, with the total checked to equal 1 — used in Raoult's law, gas mixtures and thermodynamic analysis.

Science

Enter n and the tool returns the n-th Catalan number Cₙ = (2n)! / ((n+1)! · n!) — the textbook count for balanced parentheses, binary tree shapes, Dyck paths and many other combinatorics problems.

Math

Enter a TV or monitor diagonal and an aspect ratio (e.g. 16:9, 21:9) and the tool returns the actual width, height and area in both inches and centimetres — handy for furniture planning, wall-mount fit and seeing why a "55-inch" is so much bigger than a "50-inch" in area.

Lifestyle

Enter mass, frontal area, drag coefficient and air density and the tool returns the terminal velocity v_t = √(2mg / (ρ·A·Cd)) — the speed at which drag balances gravity, with presets for skydivers, raindrops, baseballs and feathers.

Science

Enter a column of actual values and a column of predicted values; the tool computes MAE, MSE, RMSE, R² and MAPE side-by-side — the staple set of regression-error metrics in machine learning, forecasting and lab-vs-model comparisons — and explains how each one weights outliers differently.

Math

Enter the 6 coefficients of ax + by = e and cx + dy = f. The tool applies Cramer's rule to return x, y, the determinant D and the system's classification (unique solution / no solution / infinitely many), showing the working out so it doubles as a homework check.

Math

Enter applied force, cross-sectional area, original length and the change in length. The tool returns the engineering stress σ, strain ε, Young's modulus E = σ/ε and the elongation, alongside a reference table of common materials (steel, copper, aluminium, concrete, rubber).

Science

Enter net operating income (NOI) and total annual debt service (principal + interest); the tool reports the debt service coverage ratio DSCR = NOI / debt service — the headline risk metric banks use when underwriting commercial property loans, business loans and investment-property mortgages.

Finance

Enter a mass (or energy) and the tool uses Einstein's E = mc² to compute the other side, expressing the result in joules, kilowatt-hours, megatonnes of TNT and electron-volts — and showing just how staggering even 1 g of fully-converted matter is.

Science

Enter a per-trial probability p and a trial count n; the tool returns the probability of at least one success 1 − (1 − p)ⁿ, the expected count np, and the trials needed to reach a target probability — the maths behind raffles, gacha pulls, A/B tests and redundancy design.

Math

Enter a share price and EPS — the tool returns the price-to-earnings ratio P/E, the earnings yield (EPS ÷ price), and the PEG ratio (if a growth rate is supplied), then puts the result in context with typical industry bands.

Finance

Enter elevation, velocity and pressure at two points and the tool applies P + ½ρv² + ρgh = constant from Bernoulli's equation to solve for the missing variable — the foundation of pipe flow, Venturi meters, Pitot tubes and aerofoil lift.

Science

Enter total liabilities and shareholders' equity to get the D/E ratio, equity multiplier and debt-to-assets ratio, with industry context (utilities, tech, banking) to flag whether the firm's capital structure is conservative or aggressive.

Finance

Enter next year's dividend D₁, the required return r and the perpetual growth rate g; the Gordon dividend-discount model returns the intrinsic price P = D₁ / (r − g) and the growth rate implied by today's market price.

Finance

Enter net income, revenue, assets and equity; the tool applies the 3-factor DuPont identity to decompose ROE = Net Margin × Asset Turnover × Equity Multiplier, so you can see whether high returns come from profitability, efficiency or leverage.

Finance

Enter the spring constant k and mass m; the tool returns the simple-harmonic period T = 2π√(m/k), frequency f and angular frequency ω, and can also solve for k — the foundation of physics labs, mechanical vibration and MEMS sensor design.

Science

Enter observed and expected counts; the tool computes the chi-square statistic χ² = Σ (O − E)² / E, degrees of freedom and the p-value to test whether the observed distribution deviates significantly from theory — the standard test for die fairness, Mendelian ratios and categorical A/B counts.

Math

Enter resistance R and capacitance C; the tool returns the RC circuit time constant τ = R × C, the 63.2% / 99.3% charging times (1τ / 5τ) and the voltage percentage at any time t during charging or discharging — the workhorse for electronics design, RC filters, oscillator timing and Arduino debounce.

Science

Enter current assets (cash, receivables, inventory) and current liabilities (short-term debt, payables) to get the current ratio = CA ÷ CL, with industry-standard thresholds (< 1 warning, 1–2 healthy, > 3 idle cash) to flag short-term solvency at a glance.

Finance

Enter cash, marketable securities, receivables and current liabilities; the tool returns the quick ratio = (CA − inventory − prepaid expenses) ÷ CL, a stricter view of liquidity than the current ratio because it excludes inventory and prepayments that may not convert to cash quickly.

Finance

Enter net income and shareholders' equity (beginning / ending / average); the tool returns ROE = net income ÷ equity with the conventional bands (< 5% weak, 10–15% healthy, > 20% excellent), so you can read management's efficiency at deploying equity capital at a glance.

Finance

Enter hot-reservoir temperature T_h and cold-reservoir T_c (units auto-handled in °C / K / °F); the tool returns the Carnot maximum efficiency η = 1 − T_c / T_h, the thermodynamic upper bound for any real heat engine — IC engines, thermal power stations and refrigerators.

Science

Enter share price and book value per share (or total equity + shares outstanding); the tool returns P/B = price ÷ book value and benchmarks it against typical banks, insurers, real estate and SaaS bands — a core value-investing screen used since Benjamin Graham.

Finance

Enter annual demand D, ordering cost per order S and holding cost per unit per year H; the tool applies the Wilson formula Q* = √(2DS / H) to return the optimal order quantity, order frequency and total inventory cost — the classic recipe for stock-keeping and supply-chain planning.

Finance

Enter operating income (EBIT) and total revenue; the tool returns the operating margin = EBIT ÷ revenue, then benchmarks the result against software, branded consumer, manufacturing, retail and airline norms — the cleanest single read on core operating efficiency.

Finance

Enter outcome values x and matching probabilities p; the tool returns the expected value E[X] = Σ p·x, variance Var(X) and standard deviation σ — the foundational metric for casino games, insurance pricing, investment decisions and A/B-test analysis.

Math

Enter any one of linear speed, radius, period, frequency or RPM; the tool interconverts angular velocity ω (rad/s), frequency f (Hz), period T, revolutions per minute (RPM) and rim speed v — for circular motion problems, motor specs, orbital mechanics, centrifuges and any spinning object.

Science

Enter the risk-free rate Rf, expected market return Rm and the stock's beta β; the CAPM formula r = Rf + β·(Rm − Rf) returns the required rate of return (cost of equity) and breaks out the equity risk premium component (ERP × β).

Finance

Enter two particle masses m₁ and m₂; the tool applies the reduced-mass formula μ = m₁·m₂ / (m₁ + m₂) to give the effective inertial mass for two-body problems — the building block that reduces orbital mechanics, Keplerian motion, vibrational spectroscopy and collision analysis to single-body equations.

Science

Enter annual cost of goods sold (COGS) and average inventory; the tool returns the inventory turnover ratio (Turnover = COGS ÷ Avg Inventory) and days inventory outstanding (DIO = 365 ÷ Turnover) — the standard lens for retail, manufacturing and e-commerce to gauge stocking efficiency and working-capital tie-up.

Finance

Enter sample size n, sample proportion p (or sample standard deviation) and a confidence level (90 / 95 / 99 %); the tool computes the margin of error MOE = z·√(p(1−p)/n) and the matching confidence interval — the core statistic behind political polls, A/B tests and market research.

Math

Enter a series of periodic returns and a target return (often 0 or the risk-free rate); the tool returns the Sortino ratio = (R̄ − T) ÷ DD, where DD is downside deviation — a risk-adjusted return measure that captures only "bad" volatility (often preferred over the Sharpe ratio) — and annualises it based on the chosen frequency.

Finance

Enter systolic (SBP) and diastolic (DBP) blood pressure; the tool returns the pulse pressure and mean arterial pressure (MAP), then classifies the result as low / normal / elevated using the < 40, 40–60 and > 60 mmHg bands — the textbook signal for cardiovascular risk on a routine BP report.

Health

Enter a wavelength or frequency; the tool applies the Planck relation E = hf = hc/λ to return the energy of a single photon in joules and electron-volts (eV), plus the visible-light colour band where applicable — the foundation of physics, chemistry and spectroscopy problems.

Science

Enter portfolio return, risk-free rate and beta; the tool returns the Treynor ratio = (Rp − Rf) / β — excess return per unit of market (systematic) risk. It is the β-based analogue of the Sharpe ratio and is favoured for evaluating diversified portfolios and fund managers.

Finance

Enter days inventory outstanding (DIO), days sales outstanding (DSO) and days payable outstanding (DPO); the tool returns the cash conversion cycle — the number of days between paying suppliers and collecting from customers, a key measure of working-capital efficiency.

Finance

Enter serum creatinine, age and sex; the tool applies the 2021 NKF / ASN-recommended CKD-EPI formula (race-free) to estimate glomerular filtration rate (eGFR) and classifies the result into CKD stages G1–G5 — the standard reading of a kidney-function lab report.

Health

Enter age, weight, serum creatinine and sex; the tool applies the 1976 Cockcroft–Gault formula to estimate creatinine clearance (CrCl, mL/min) — still the FDA- and EMA-required formula for renal dose adjustment in most drug labels.

Health

Enter your birth date and target retirement age; the tool returns the exact years, months, days and total days remaining until retirement, plus the calendar date you will retire — useful for financial and life planning.

Date & Time

Enter the P/E ratio and the expected annual EPS growth rate (%); the tool returns the PEG ratio = P/E ÷ growth, popularised by Peter Lynch — a more honest valuation read for growth stocks than the P/E alone.

Finance

Enter a blackbody temperature in kelvin; the tool applies Wien's displacement law λ_max·T = b to return the peak wavelength and corresponding frequency, and can invert to estimate temperature from a measured wavelength — the foundation of solar spectra, thermal imaging and CMB analysis.

Science

Enter latitude, longitude and date; the tool applies the NOAA solar position algorithm to return local sunrise, sunset and solar-noon times, plus the length of the day — essential for photography, outdoor activities, agriculture and solar-energy planning.

Date & Time

Enter waist circumference and height in any units; the tool returns the waist-to-height ratio (WHtR) and classifies it against the universal "keep your waist to less than half your height" cut-off (< 0.5) — a more sensitive central-obesity signal than BMI.

Health

Enter initial length L₀, temperature change ΔT and the linear expansion coefficient α (or pick a preset material); the tool returns ΔL = α·L₀·ΔT and the new length — used for bridge expansion joints, rail track gaps, pipework thermal allowances and more.

Science

Enter EBIT and interest expense; the tool returns the interest-coverage ratio (also called Times Interest Earned) — a core credit metric used by rating agencies and lenders to judge a firm's ability to service its debt.

Finance

Enter initial and final angular velocity plus the time interval (or tangential acceleration and radius); the tool returns the angular acceleration α and converts between rad/s² and rpm/s — a basic quantity in rotational dynamics, rotor engineering and motor analysis.

Science

Enter a list of numbers; the tool returns the mean absolute deviation (MAD = average of |xᵢ − mean|) — a more intuitive spread measure than standard deviation, used in school statistics and demand-forecasting accuracy.

Math

Enter your entry price, target and stop-loss; the tool returns the reward-to-risk ratio and the minimum win-rate required to break even — the headline check every trader runs before sizing a position.

Finance

Computes the pediatric maintenance IV fluid rate (mL/hr and mL/day) from body weight using the Holliday-Segar 4-2-1 rule — the standard since the original 1957 publication.

Health

Enter total cholesterol, HDL and triglycerides; the Friedewald equation (LDL = TC − HDL − TG / 5 or / 2.2 SI) estimates LDL-C and grades the result by NCEP ATP III risk bands.

Health

Paste a price or NAV series and the tool returns the maximum drawdown (MDD), peak, trough, drawdown duration and recovery time — the benchmark downside-risk metric for any strategy.

Finance

Paste (x, y) data points; the tool fits an ordinary least-squares regression and reports the coefficient of determination R², slope, intercept and Pearson r — the standard "how much variance is explained" measure.

Math

Enter any three of plane spacing d, diffraction angle θ, order n and wavelength λ; the tool solves Bragg's law nλ = 2d sinθ for the missing one — the cornerstone of X-ray crystallography and materials characterisation.

Science

Enter base dimensions and height; the tool returns volume, base area, slant height, lateral surface area and total surface area for square, rectangular, equilateral-triangular or regular n-gon based right pyramids using V = ⅓ × base area × height.

Math

Enter base and height, or two side lengths and the included angle; the tool returns the parallelogram area, perimeter and both diagonals via A = b · h or A = a · b · sin θ.

Math

Enter the semi-major axis a and semi-minor axis b; the tool returns the area A = π a b and uses Ramanujan's second approximation for the perimeter — relative error below 4 × 10⁻⁵ across all eccentricities.

Math

Enter the optimistic (O), most-likely (M) and pessimistic (P) estimates; the tool applies the PERT beta-distribution formulas E = (O + 4M + P)/6 and σ = (P − O)/6, and reports the 1σ / 2σ / 3σ confidence ranges for project duration or cost.

Finance

Enter any distance and the tool converts it across metres, kilometres, miles, Earth–Moon distance, astronomical units (AU), light-years, parsecs and light-travel time — useful for astronomy, science fiction and classroom prep.

Conversion

Enter initial velocity u, final velocity v and elapsed time t; the tool returns the average acceleration a = (v − u) / t along with the displacement s = ½(u + v)·t — the entry-point of Newtonian kinematics.

Science

Enter a Z-score; the tool returns the one-sided (left / right) and two-sided p-values, and flags significance against α = 0.05 / 0.01 / 0.001 — the missing step of nearly every hypothesis test.

Math

Enter the sphere radius R and cap height h; the tool returns V = πh²(3R − h)/3 and the curved surface area A = 2πRh — useful for partial spherical tanks, domes and lens segments.

Math

Enter a scale ratio (e.g. 1:25 000) and a measured map distance; the tool returns the real-world distance, or works in reverse from real distance to map distance — useful for hiking, map reading and town planning.

Conversion

Enter a particle's mass and speed; the tool applies the de Broglie relation λ = h / (mv) to return the matter-wave wavelength, momentum and kinetic energy — the cornerstone of intro quantum mechanics, electron-microscope resolution and cold-neutron experiments.

Science

Paste a list of values; the tool scans the dataset and reports the most-frequent value(s), handling unimodal, bimodal and multimodal cases, with the full frequency table — the standard intro-statistics tool for categorical and discrete data summaries.

Math

Enter a date and your fiscal-year start month; the tool reports the calendar quarter (Q1–Q4), the fiscal quarter and fiscal-year label, the quarter's start/end dates and the percentage of the quarter elapsed — useful for SEC filings, government budgets and SaaS subscription planning.

Date & Time

Enter face value, coupon rate, years to maturity and current market price; the tool bisects for the bond's yield to maturity (YTM), current yield and total coupon cash flows — the discount-rate benchmark used in bond pricing, credit-spread analysis and retirement-portfolio planning.

Finance

Enter a mass in kilograms, solar masses or Earth masses; the tool applies r_s = 2GM/c² to return the Schwarzschild radius (event horizon) and equivalent density — the headline number for any black-hole conversation in astrophysics, GR intro courses and pop-science Q&A.

Science

Enter great-circle distance (km / mi / nm), cabin class and segment type (domestic / short / long-haul); the tool applies DEFRA 2024 emission factors to estimate per-passenger CO₂-equivalent kilograms, total trip emissions and tree-month offsets — the standard checklist for business-travel reporting, personal carbon budgets and offset-purchase decisions.

Lifestyle

Enter an amount and a VAT / GST rate; the tool computes both directions — adding tax to a net price, and extracting the tax already embedded in a gross price. Works for any country that uses VAT / GST / IVA / TVA (UK 20%, EU 17–27%, AU & SG GST, India GST, etc.).

Lifestyle

Enter net operating income (NOI) and property value to get the capitalization rate (NOI ÷ value). The tool also solves in reverse — give it any two of {cap rate, NOI, value} and it derives the third — the standard yardstick real-estate investors use to compare property yields.

Finance

Enter battery capacity (in Wh or Ah + voltage), load power, depth of discharge and inverter efficiency; the tool returns the realistic usable runtime in hours. Use it to size UPS units, solar-storage banks, portable power stations and 12 V car fridges.

Science

Enter your current weight, target weight and daily calorie deficit; the tool uses the "≈ 3 500 kcal per lb of body fat" rule of thumb to project the number of weeks and the expected date you will reach your goal — a sanity check for setting a sustainable pace.

Health

Enter face value, coupon rate, term, payment frequency and yield-to-maturity; the tool returns the Macaulay duration (the cash-flow-weighted average years to maturity) and modified duration (the % price drop for a 1 % rise in yield) — the standard measures of a bond's interest-rate risk.

Finance

Enter daily energy use (kWh), peak sun hours, panel wattage and overall system efficiency; the tool returns the required array size in kW and the number of panels needed — a starter sizing tool for rooftop PV, off-grid cabins and RV / van conversions.

Lifestyle

Enter the total current and two parallel resistor values; the tool applies the current-divider rule I₁ = I·R₂/(R₁+R₂) to compute each branch current, the equivalent resistance, the shared voltage and the power dissipated in each resistor — a staple for circuit analysis, PCB design and EE coursework.

Science

Enter initial value N₀, continuous rate constant k and elapsed time t; the tool returns N(t) = N₀·e^(kt), the per-period change, and the doubling time (k > 0) or half-life (k < 0) — the universal model for populations, bacteria, radioactive decay, first-order pharmacokinetics and continuously compounded interest.

Math

Enter gross monthly income, existing monthly debt, mortgage rate and term; the tool applies the lending-industry 28 / 36 rule to estimate the maximum PITI you can afford and the corresponding home price — a universal pre-shopping affordability screen.

Finance

Enter room L × W × H and target air changes per hour; the tool returns the required ventilation airflow in CFM, m³/h and L/s. Built-in ASHRAE 62.1 presets (bedroom, kitchen, conference room, gym, etc.) make it easy to size extract fans, supply diffusers and HEPA purifiers.

Lifestyle

Enter inductance L and frequency f; the tool returns the inductive reactance X_L = 2πfL and the angular frequency ω — used in filter design, impedance matching and AC circuit analysis.

Science

Enter the object speed and the local air temperature (the tool derives a from temperature); returns the Mach number M = v ⁄ a and classifies the regime as subsonic, transonic, supersonic or hypersonic — a standard tool for aviation and fluid dynamics.

Science

Enter current salary or pension, the year-over-year change in CPI and the COLA formula to apply; the tool returns the inflation-adjusted new amount and real purchasing power — used for contract renewals, pension uplifts and year-on-year comparisons.

Finance

Enter the standard deviation of daily, weekly or monthly returns; the tool applies the √N rule σ_annual = σ_period × √N to give the annualised volatility — the standard preprocessing step for Sharpe ratio, option pricing and risk reports.

Finance

Pick a pulley configuration (fixed, single movable, block-and-tackle or differential), enter the load; the tool returns the input force required, ideal & actual mechanical advantage and the rope length pulled — staple tool for physics class and rigging.

Science

Enter the enthalpy change ΔH, entropy change ΔS and absolute temperature T; the tool applies ΔG = ΔH − TΔS to give the free-energy change and flags whether the reaction is spontaneous (ΔG < 0), at equilibrium (ΔG = 0) or non-spontaneous (ΔG > 0) — a staple of chemical thermodynamics, biochemistry and materials science.

Science

Enter any positive integer n; the tool iterates the Collatz rule (even → n/2, odd → 3n+1) until it reaches 1 and lists the full sequence, the number of steps and the peak value reached — a classic number-theory and programming exercise.

Math

Enter two price–quantity pairs; the tool applies the midpoint (arc) formula Ed = (ΔQ ⁄ Q̄) ⁄ (ΔP ⁄ P̄) and classifies demand as elastic, unit-elastic or inelastic — a staple of microeconomics, pricing decisions and tax-incidence analysis.

Finance

Two-way conversion between degrees–minutes–seconds (D° M′ S″) and decimal degrees — the standard need when juggling GPS coordinates, astronomy, surveying and marine navigation. Supports signed values for south latitude and west longitude.

Conversion

Paste a series of values (prices, sales or any time-series) and a window length N; the tool returns the simple moving average point-by-point via SMA_t = (x_{t−N+1} + … + x_t) ⁄ N — staple of technical analysis, demand smoothing and KPI dashboards.

Finance

Enter specific impulse Isp, initial mass m₀ and final (dry) mass m_f; the tool applies Δv = Isp · g₀ · ln(m₀ ⁄ m_f) to give the ideal velocity change a rocket can deliver — fundamental for mission planning, orbital mechanics and Kerbal Space Program players alike.

Science

Enter a positive integer n and the tool returns the n-th triangular number Tₙ = n(n+1)/2, or inversely: given any positive integer N, identify whether N is triangular (and at which index) — staple of combinatorics, the handshake problem and math competitions.

Math

Enter the wavelength or frequency of incident light plus the metal's work function φ; the tool applies Einstein's photoelectric equation KE = hf − φ to give the maximum kinetic energy of ejected electrons, the stopping voltage V₀ and whether the threshold frequency is met.

Science

Enter a tax-exempt bond yield (e.g. US municipal bonds) and your marginal tax rate; the tool applies TEY = tax-free yield ⁄ (1 − tax rate) to give the equivalent pre-tax yield a taxable bond must offer to match it — the standard yardstick for comparing investments with different tax treatments.

Finance

Enter chainring teeth, sprocket (cog) teeth and wheel size (700C, 26", 29er, etc.); the tool returns classic gear inches, metres of development and speed for any cadence — cyclists' go-to comparison for climbing-friendly vs. high-speed gear setups.

Lifestyle

Enter a positive integer n; the tool applies Σᵢ₌₁ⁿ i² = n(n+1)(2n+1)/6 to return the sum of the first n squared positive integers, along with the sum of cubes ([n(n+1)/2]²) and the arithmetic sum — fundamental identities for induction, series and statistics problems.

Math

Enter any length and the tool splits it into long / short parts so that a/b = (a+b)/a using the golden ratio φ ≈ 1.6180339887, or inversely: input two segments and see how closely their ratio approaches φ — a staple of design, photography, layout and mathematics.

Math

Enter the material thermal conductivity k, area A, thickness L and temperature difference ΔT; the tool applies Fourier's law Q = k·A·ΔT / L to give the steady-state heat flow (W) and derives the R-value (thermal resistance) — fundamental for wall insulation, glazing, CPU heatsink and energy-audit calculations.

Science

Paste a list of incomes / wealth / sales values; the tool computes the Gini coefficient via G = Σ|xᵢ − xⱼ| / (2 n² · mean) (0 = perfect equality, 1 = total inequality) and reports the Lorenz curve and cumulative distribution — used in economics, sociology and sales-concentration analysis.

Finance

Enter the parallel fraction p of a program and the number of processors N; the tool applies Amdahl's law S = 1 / ((1 − p) + p ⁄ N) to give the theoretical maximum speedup — essential for parallel computing, GPU programming, HPC capacity planning and data-engineering decisions.

Science

Enter the hang time of a jump (seconds); the tool applies the free-fall formula h = ⅛ g t² to give the vertical jump height (cm), and also reports the take-off velocity and apex time — used in basketball, volleyball, plyometric training and fitness testing.

Lifestyle

Enter the signal and noise power (or voltage); the tool applies SNR(dB) = 10·log₁₀(P_s ⁄ P_n) or 20·log₁₀(V_s ⁄ V_n) and classifies the result for communications, audio or instrumentation use — fundamental for telecom, recording and measurement.

Science

Enter the activation energy Eₐ, pre-exponential factor A and temperature T; the tool returns the reaction rate constant k via Arrhenius k = A·exp(−Eₐ ⁄ RT) and the rate ratio between two temperatures — the standard tool for chemical kinetics, food shelf-life and drug stability.

Science

Enter two sides and the included angle (SAS) or three sides (SSS); the tool applies c² = a² + b² − 2ab·cos C to solve the unknown side or angle and reports all three sides and angles — a core surveying, construction and navigation tool.

Math

Enter pre / post-exercise body weight, fluids consumed and session length; the tool returns sweat rate per hour (L/h) and a suggested fluid intake every 15 minutes per the ACSM hydration guidelines — used by runners, cyclists, footballers and recruits.

Health

Enter your head circumference (cm or inches); the tool maps it to US (fitted and fractional), UK, EU (cm) and Japanese hat sizes plus the S/M/L/XL range — useful for buying New Era caps, fedoras, baseball caps and helmet liners online.

Conversion

Enter weekly hours, annual leave days and public holidays; the tool returns net annual working hours after leave and converts a yearly salary into hourly, daily and monthly rates — useful for freelancers, contractors and HR cost planning.

Date & Time

Enter the number of teams or players; the tool returns total matches and rounds for single-elimination (N − 1), double-elimination, single round-robin (N·(N−1)/2) and double round-robin formats, plus the number of byes in the knockout bracket — useful for tournament scheduling in sports, board-game leagues and esports.

Lifestyle

Enter after-tax monthly income; the tool applies the 50/30/20 rule (Elizabeth Warren) and splits it into needs (50%), wants (30%) and savings/debt repayment (20%) — the most widely taught starter budget framework in personal finance.

Finance

Enter total swim time and distance (metres or yards); the tool returns pace per 100 m (or 100 yd) and predicts completion time for any target distance — essential for pool training, triathlon and masters racing.

Lifestyle

Enter your enrolled credit hours and a study-per-credit ratio (the 2–3 hr/credit/week guideline used by most universities); the tool returns total weekly study time and projects total semester hours over a 14-week term — a standard time-management aid for college students.

Education

Enter two players' Elo ratings (chess, online games or any Elo-style ladder); the tool uses the FIDE formula E = 1 ⁄ (1 + 10^((Rb − Ra) ⁄ 400)) to return each player's expected score and the rating change after a chosen result and K-factor — used by chess players, esports competitors and Glicko/USCF tournament preparation.

Lifestyle

Enter your essential monthly expenses and target coverage (3, 6 or 12 months); the tool returns the total emergency fund target, the gap from your current balance and the months needed to reach the target at your monthly savings rate — a cornerstone of personal-finance and FIRE planning.

Finance

Enter a drink's volume (ml) and alcohol content (ABV %); the tool converts to standard drinks using each region's definition (US 14 g, UK 8 g, AU/HK 10 g, JP 20 g of pure alcohol) and compares with WHO and national low-risk guidelines (e.g. ≤ 10 drinks/week).

Health

Enter board thickness (in), width (in) and length (ft); the tool applies BF = (T × W × L) ⁄ 12 to return board feet per piece, total board feet, volume (ft³ / m³) and total cost — used by woodworkers, furniture makers and DIY hobbyists for lumber budgeting.

Math

Enter total fence length, spacing between posts and number of gates; the tool returns post count (line + corner + end), rail count and panel sections — the classic "fence-post problem" reduced to one click for homeowners, farms and contractors estimating materials.

Lifestyle

Enter room length, width and height, opening (door / window) area, sheet size (4×8, 4×10 or 4×12 ft) and waste factor; the tool returns sheets needed, total square footage and estimated screws, joint tape and joint compound — a quoting tool for DIY remodels and drywall contractors.

Lifestyle

Enter the intensity at one distance; the tool applies I₂ = I₁ × (d₁ ⁄ d₂)² to return intensity at any other distance, along with the equivalent dB change (ΔL = 20·log₁₀(d₁ ⁄ d₂)) — a workhorse for photography, stage lighting, audio engineering, radiation safety and radio link planning.

Science

Enter height and waist circumference; the tool applies the Thomas (2013) Body Roundness Index BRI = 364.2 − 365.5·√(1 − ((WC/2π) ⁄ (0.5·h))²). BRI tracks visceral fat and metabolic-disease risk more closely than BMI — a JAMA 2024 study linked BRI to cardiovascular mortality.

Health

Enter the length, width and thickness of a driveway or road; the tool uses the density of hot-mix asphalt (~2.4 t/m³) to return tonnage and converts inch/foot inputs to metric tonnes — a quoting tool for DIY homeowners, HOAs and paving contractors.

Lifestyle

Enter the three sides a, b, c of a triangle; the tool applies r = A ⁄ s (inradius) and R = abc ⁄ (4A) (circumradius) to return both circle radii, plus triangle area via Heron's formula — a workhorse for geometry homework, mechanical layout and architectural design.

Math

Enter base a, exponent b and modulus n; the tool uses the square-and-multiply fast-exponentiation algorithm with BigInt support to compute a^b mod n — the core operation behind RSA cryptography, hashing and modular-arithmetic homework.

Math

Enter current, one-way wire length, conductor size (AWG) and system type (single-phase / three-phase); the tool returns voltage drop and % drop via V_drop = 2·I·R·L (1-φ) or √3·I·R·L (3-φ) and warns when it exceeds the NEC 3% guideline — essential for home wiring, solar runs and long-distance equipment feeds.

Science

Convert between kilowatt (kW), mechanical horsepower (HP), metric horsepower (PS / cheval-vapeur), brake horsepower (BHP), and foot-pound-force per second — the standard unit set for cars, engines, generators and power tools across UK / US / EU / JP markings.

Conversion

Enter capacitance C and frequency f; the tool returns the capacitive reactance X_C = 1/(2πfC) and the angular frequency ω — used for filter design, AC circuit analysis and impedance matching, complementing the existing inductor reactance tool.

Science

Enter a and modulus n; the tool uses the extended Euclidean algorithm to return the modular inverse (a·x ≡ 1 mod n), gcd(a, n) and the Bézout identity — required for RSA private-key generation, the Chinese Remainder Theorem and solving linear congruences.

Math

Enter the luminous flux (lumens, lm) of a fixture and the lit area; the tool returns the illuminance (lux = lm/m²) and can solve for the lumens required to hit a target lux — used for room lighting design, photography, grow lights and workplace illuminance planning.

Conversion

Enter pet weight, species (dog or cat), life stage and activity level; the tool uses the NRC Resting / Maintenance Energy Requirement formulas to compute daily calorie needs and the matching dry-food portion (grams/day) — the standard tool for pet owners.

Lifestyle

Enter a Gregorian year and the tool returns the dates and UTC times of the spring equinox, summer solstice, autumn equinox and winter solstice using Jean Meeus’ astronomical formulas — useful for gardening, festival planning, photography and the Chinese solar-term calendar.

Date & Time

Recipe calls for pan A but you only have pan B? Enter both pans (round / square / rectangular) and the tool returns the ingredient scale factor by volume ratio plus a suggested bake-time adjustment — works across all common pan shapes.

Lifestyle

Enter screen diagonal (inches) and resolution (1080p / 4K / 8K); the tool returns optimal and maximum viewing distance based on SMPTE 30°, THX 36° field-of-view recommendations and human visual acuity — the standard tool for sizing a new TV or arranging your couch.

Lifestyle

Enter your birth date; the tool returns your age on Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune using each planet's orbital period — a popular STEM / classroom / museum tool that turns abstract astronomy into a fun, personal number.

Date & Time

Enter face value, coupon rate, yield to maturity, years to maturity and coupon frequency; the tool returns bond convexity, modified duration and a second-order price-change estimate for an interest-rate move — the standard tool for fixed-income portfolio risk management.

Finance

Enter the gasoline volume and the desired ratio (25:1, 32:1, 40:1, 50:1, etc.); the tool returns the exact two-stroke oil quantity in mL and US fl oz — works for chainsaws, weed trimmers, outboard motors, two-stroke motorbikes, leaf blowers and any other two-stroke engine.

Lifestyle

Enter mass, incline angle and coefficient of friction; the tool applies Newton's second law to return net force along the slope, acceleration, normal force and the push needed to hold or move the object — a staple for high-school / first-year physics and basic mechanical design.

Science

Enter the two masses m₁ and m₂ hung from a fixed pulley; the tool returns the system acceleration via a = (m₁ − m₂)g ⁄ (m₁ + m₂), the rope tension T and the heavier-mass direction — the standard quick-reference for a classic mechanics textbook problem.

Science

Enter your prior cumulative GPA and credits already earned, then this term's GPA and credits attempted; the tool weights the two and reports your new cumulative GPA — the standard "what will my GPA be after this term?" planner.

Education

Enter the drop height h and the rebound height h′; the tool applies e = √(h′ ⁄ h) to compute the coefficient of restitution (COR), the energy-loss percentage and the post-impact/pre-impact speed ratio — the standard tool for physics labs and sports engineering (tennis, basketball, golf).

Science

Enter an IPv4 address and CIDR prefix length (e.g. 192.168.1.10/24); the tool returns the subnet mask, network address, broadcast address, usable host range and total host count — a daily tool for network admins and SREs.

Math

Enter two masses m₁, m₂ and pre-collision velocities v₁, v₂; the tool applies momentum conservation m₁v₁ + m₂v₂ = (m₁ + m₂)v′ to find the common post-collision velocity, plus energy lost (to heat/sound/deformation) and pre/post kinetic energies — the standard tool for physics class and accident-reconstruction.

Science

Enter your annual spending and safe withdrawal rate (default 4%); the tool returns the portfolio size needed for financial independence via FIRE = annual spending ÷ SWR, plus Lean / Coast / Fat FIRE benchmarks — the core tool for the FIRE movement and any long-term retirement plan.

Finance

Enter the estimated due date or the last menstrual period (LMP); the tool applies the Naegele rule in reverse to estimate the conception date and fertile window (5 days before to day of ovulation), supporting due dates derived from ultrasound CRL — useful for prenatal planning and medical records.

Date & Time

Enter the split or reverse-split ratio (e.g. 4-for-1, 1-for-10), original share count and share price; the tool returns the post-split share count, adjusted price and total market value (unchanged) — works for backtesting historical prices and is the standard adjustment in equity research and ETF tracking.

Finance

Enter a numerator and denominator (e.g. 48 ⁄ 60); the tool reduces to lowest terms via the greatest common divisor (4 ⁄ 5) and also shows the mixed-number, decimal and percent equivalents — a workhorse for primary and middle-school maths homework.

Math

Enter wheel diameter (or circumference) and RPM (or speed); the tool applies C = π·d to return rolling distance per revolution, distance per minute and the matching road speed (km/h, mph) — useful for bikes, cars, conveyors, gears and physics class.

Conversion

Enter a row index n (starting at 0); the tool prints the binomial coefficients C(n,0) C(n,1) … C(n,n) for that row, along with the row sum 2ⁿ, the maximum value and the matching (a+b)ⁿ expansion — a quick reference for combinatorics, binomial distributions and the binomial theorem.

Math

Enter visual acuity in Snellen (20/20, 20/40, etc.), metric Snellen (6/6, 6/12), LogMAR or decimal; the tool returns the other three formats with reference thresholds for driving licences and the legal-blindness cut-off — the standard conversion for ophthalmology, optometry and driving / occupational medicals.

Health

Enter a Gregorian date or a Hijri (Islamic) date; the tool converts between the two using the tabular Umm al-Qura algorithm (also known as the Kuwaiti algorithm) — useful for Islamic festivals (Ramadan, Hajj, Eid), cross-cultural documents and historical records.

Date & Time

Enter image pixels (e.g. 24 MP or 6000 × 4000) and target print resolution (300 DPI photo, 240 DPI relaxed, 150 DPI poster); the tool returns the maximum print size in inches and cm, and works in reverse to find the megapixels needed for a desired print — a workhorse for photo printing, poster design and album layout.

Conversion

Tick the burned regions (head, anterior / posterior torso, arms, legs, perineum) and the patient age group (adult / child); the tool applies Wallace's Rule of Nines to return total body-surface-area burned (%TBSA) and shows the Parkland fluid-resuscitation target — the standard field tool in emergency medicine, fire-rescue and first-aid.

Health

Enter two angles + one side (AAS / ASA) or two sides + one non-included angle (SSA — including the ambiguous case); the tool applies sin A ⁄ a = sin B ⁄ b to solve the unknown side or angle and reports all three sides, angles and area. Pair with the existing Law of Cosines tool to cover every SAS / SSS / AAS / ASA / SSA triangle-solving case.

Math

Enter the first cash flow, growth rate g, discount rate r and number of periods n; the tool returns PV = C × [1 − ((1+g) ⁄ (1+r))ⁿ] ⁄ (r − g). Used to value salary packages with annual raises, commercial real-estate leases with rent escalators, and inflation-adjusted retirement withdrawals.

Finance

Enter two temperatures plus one saturation vapor pressure (and the molar enthalpy of vaporisation ΔHvap); the tool applies ln(P₂ ⁄ P₁) = −ΔHvap ⁄ R × (1 ⁄ T₂ − 1 ⁄ T₁) to return the vapor pressure at the other temperature, or the boiling point at altitude. A staple of chemistry, HVAC, brewing, cooking and meteorology.

Science

Paste a dataset (comma-separated); the tool returns mean, median, mode, sample standard deviation, plus Pearson's First skewness coefficient (uses the mode) and Second skewness coefficient (uses the median, 3·(mean − median) ⁄ SD) — the standard quick measure of distribution asymmetry in data science, quality control and psychometrics.

Math

Paste a dataset; the tool returns Q1, Q3 and the IQR, then applies Tukey's 1.5 × IQR rule to flag mild outliers (beyond ±1.5 IQR of the quartiles) and extreme outliers (beyond ±3 IQR), reporting the box-plot whisker range. A standard step in exploratory data analysis, quality control and data cleaning.

Math

Enter body weight, sex and the powerlifting total (squat + bench + deadlift, in kg or lb); the tool applies the Wilks 2020 coefficients to return the Wilks score — the standard way to compare powerlifters across body-weight classes and sexes, and the basis of best-lifter awards in IPF, USAPL and many federations.

Health

Enter a cash-flow stream (negatives for outflows, positives for inflows), a reinvestment rate and a finance rate; the tool returns MIRR = (FV of positive flows ⁄ |PV of negative flows|)^(1 ⁄ n) − 1. MIRR fixes IRR's flawed implicit-reinvestment assumption and is the standard ranking metric in Excel's MIRR() function, Brealey-Myers-Allen and the CFA curriculum.

Finance

Enter the initial outlay, the future cash-flow stream and a discount rate; the tool returns PI = PV of future cash flows ⁄ |Initial Investment|. The standard ranking metric under capital rationing — PI > 1 means the project creates value, equivalent in sign to NPV but expressed as "PV created per dollar invested".

Finance

Enter the solute mass, molar mass, solvent mass, the solvent freezing-point depression constant Kf and the van't Hoff factor i; the tool applies ΔTf = i · Kf · m to return the temperature drop and the new freezing point. A staple of general chemistry, food science, road de-icing and antifreeze formulation.

Science

Enter the redshift z and the Hubble constant H₀ (default Planck 2018 value 67.4 km/s/Mpc); the tool returns recession velocity v = cz, comoving distance d = v ⁄ H₀, and the relativistic-Doppler form v_rel = c · ((1+z)² − 1) ⁄ ((1+z)² + 1) for high-z work. The standard back-of-the-envelope tool for estimating cosmological distances.

Science

Enter each group's mean, standard deviation and sample size; the tool returns the t statistic, degrees of freedom and two-sided p-value under both Welch's test (no equal-variance assumption) and the Student pooled t-test. The most-used inferential test for controlled experiments, A/B tests and clinical trial outcome comparisons.

Math

Enter the portfolio's annualised excess return over a benchmark and the tracking error; the tool returns IR = (Rₚ − R_b) / σ(Rₚ − R_b). The Information Ratio is the standard active-management performance metric, complementing the Sharpe Ratio.

Finance

Enter the bond face value, coupon rate, payment frequency, call price, years to call and current price; the tool numerically solves PV = Σ coupon ⁄ (1+y/m)ᵏ + Call ⁄ (1+y/m)ⁿ for YTC — the holding-period yield assuming the issuer calls the bond at the earliest call date.

Finance

Enter two paired numeric arrays; the tool converts each to ranks (averaging ties) and applies Pearson's formula on the ranks to return Spearman's ρ. A non-parametric measure of monotonic association, robust to outliers and with no normality assumption.

Math

Enter a child's birth date and a reference date; the tool returns the equivalent US K-12 grade (K, 1–12), UK / Hong Kong school year (Y1–Y13), IB Programme stage (PYP / MYP / DP) and the academic-year cut-off used. Useful for international families, school transfers and study-abroad planning.

Education

Enter room length, width (m or ft) and ceiling height; the tool consults the ASHRAE / ENERGY STAR ceiling-fan sizing guide to recommend a blade span (29″–72″) and a minimum CFM (airflow) rating, and flags whether a downrod is needed to keep the 8 ft sweet-spot height.

Lifestyle

Enter total carbohydrates, dietary fibre and sugar alcohols (per serving); the tool returns Net Carbs = total carbs − fibre − ½ × sugar alcohols. The standard keto / low-carb / diabetic-diet metric for absorbable carbs per serving.

Health

Enter the periodic growth rate r (in %); the tool returns t = ln 2 ⁄ ln(1+r), the exact number of periods needed for a quantity to double. More accurate than the Rule of 72, and applies to population, GDP, investment returns, bacterial cultures and any exponential-growth process.

Math

Enter a server's total tips for the shift and the percentage tipped out to each support role (bartender, busser, host, kitchen); the tool returns the amount sent to each role and the server's take-home tip. The standard "tip out" workflow used in US, Canadian and Australian restaurants.

Lifestyle

Enter the sample standard deviation and sample size; the tool returns SEM = s ⁄ √n and the 95% confidence interval (μ ± 1.96 × SEM). The standard calculation behind error bars in scientific charts, A/B-test reporting and journal articles.

Math

Enter two or more independent sound levels (dB); the tool combines them using L_total = 10 log₁₀(Σ 10^(Lᵢ ⁄ 10)). Explains why two equally loud machines together produce only a 3 dB increase rather than double — essential for engineering acoustics and noise assessments.

Science

Enter real power P (kW) plus either apparent power S (kVA) or the power factor cos φ; the tool computes the missing two using S² = P² + Q² and PF = cos φ, and returns the phase angle. Essential for industrial loads, motor sizing and UPS planning.

Science

Enter heart rate (HR) and stroke volume (SV); the tool computes cardiac output Q = HR × SV (L/min) and, given body surface area (BSA), the cardiac index CI = Q / BSA. Core hemodynamic math for emergency medicine, cardiology and nursing.

Health

Enter the counts of Promoters (9–10), Passives (7–8) and Detractors (0–6); the tool returns NPS = %Promoters − %Detractors on a −100 to +100 scale. The de-facto standard customer-loyalty and product-experience metric for SaaS and retail.

Lifestyle

Enter the post engagements (likes + comments + shares) and the denominator (followers, reach or impressions); the tool returns engagement rate by all three bases. Standard benchmark in influencer marketing, brand-KOL evaluation and ad-campaign reporting.

Lifestyle

Enter ARPU, gross margin, average customer lifespan and customer acquisition cost; the tool returns LTV = ARPU × margin × lifespan and the LTV / CAC ratio (industry benchmark 3×). Essential unit-economics math for SaaS, subscription and e-commerce businesses.

Finance

Common questions: "100 is 40% of what?" "After +8% it is 540 — what was the original?" The tool handles all three classic reverse-percentage cases: original from percent, percent from base, and pre-markup or pre-discount value.

Math

Enter the incident photon wavelength and scattering angle; the tool returns the Compton shift Δλ = (h ⁄ m_e c)(1 − cos θ), the scattered-photon wavelength and the photon energy loss. Cornerstone result of quantum mechanics, X-ray scattering and radiation physics.

Science

Enter a track's BPM and the tool returns the millisecond delay time for every common note value — whole, half, quarter, eighth, sixteenth, thirty-second — plus dotted and triplet variants. Essential for producers setting echo, reverb pre-delay and sidechain timing in any DAW.

Conversion

Enter your current cumulative GPA and credits earned, the credits planned for next term, and the cumulative GPA you want by end of next term. The tool returns the minimum GPA you must score next term — using (target × total credits − current GPA × earned credits) ÷ next-term credits − and flags whether the target is mathematically reachable.

Education

Enter the current cash balance, monthly operating expenses and monthly revenue; the tool returns net burn (expenses − revenue), gross burn (expenses) and runway in months (cash ÷ net burn) — the standard "when do we run out of money?" calculation for startups and VCs.

Finance

Enter weight and body-fat percentage; the tool returns BMR via the Katch-McArdle formula (BMR = 370 + 21.6 × lean body mass in kg) and TDEE after an activity multiplier. More accurate than Mifflin-St Jeor for lean and athletic body types where fat mass varies widely.

Health

Enter a date and a format (DD/MM/YYYY, MM/DD/YYYY, YYYY-MM-DD, etc.); the tool tells you whether it is a palindrome date (reads the same forwards and backwards, e.g. 22/02/2022) and lists the next five upcoming palindrome dates. A fun tool for picking wedding dates, anniversaries or other "perfectly symmetric" days.

Date & Time

Enter total ad spend, impressions, clicks and conversions; the tool returns CPM (cost per mille), CPC (cost per click), CPA (cost per acquisition) plus CTR and CVR. Foundational metrics for digital advertising — Google Ads, Meta Ads, TikTok Ads — and any media-buying budget exercise.

Finance

Enter the start-of-period customer count, end-of-period count and new customers acquired; the tool returns the churn rate, retention rate and expected average customer lifetime (1 ⁄ churn). The two most-watched health metrics for SaaS, subscription and membership businesses.

Finance

Enter the win probability p, net odds b and bankroll; the tool returns the Kelly-optimal stake fraction f* = (bp − q) ⁄ b and the suggested bet size (with optional ¼ / ½ fractional-Kelly). The standard bankroll-management framework for sports betting, poker and quant investing.

Math

Enter video duration (minutes), video bitrate (Mbps) and audio bitrate (kbps); the tool computes the resulting file size in GB ⁄ MB and runs the inverse: given a target file size, what bitrate fits. Handy for YouTube uploads, streaming budgets and estimating SD-card / cloud-storage requirements.

Conversion

Enter the child's weight (kg), prescribed dose (mg ⁄ kg ⁄ dose or mg ⁄ kg ⁄ day), dosing frequency and adult-equivalent maximum; the tool returns the per-dose and total-daily amounts and flags when the adult cap is exceeded. The bread-and-butter weight-based dosing framework used in paediatrics worldwide.

Health

Enter any time on a 12-hour clock; the tool returns the angle between the hour and minute hands using |30·H − 5.5·M|, reported as the smaller angle in the 0 – 180° range. A classic interview / math-olympiad question and a useful teaching aid for analog-clock instruction.

Math

Enter the asset cost, salvage value and useful life; the tool returns annual depreciation (cost − salvage) ÷ life, plus the accumulated depreciation and end-of-year book value for every year of the schedule. The most-used depreciation method in corporate accounting, fixed-asset registers and tax filings.

Finance

Enter primary / secondary turns (or voltages); the tool returns the turns ratio V₁ ⁄ V₂ = N₁ ⁄ N₂ = I₂ ⁄ I₁, the output voltage, the output current and the impedance reflection (N₁ ⁄ N₂)². Cornerstone of electrical engineering, audio output transformer design and power-distribution planning.

Science

Enter the number of sides n; the tool returns the sum of interior angles (n − 2) × 180°, the per-vertex interior angle in a regular polygon (sum ÷ n) and the per-vertex exterior angle (360° ÷ n). A standard high-school geometry tool and useful for tiling / tessellation design.

Math

Enter text or Morse code; the tool converts in either direction using the ITU-R M.1677-1 international Morse alphabet (letters, digits and standard punctuation), with conventional 3-space letter gaps and 7-space word gaps. Standard reference for amateur radio (HAM), scouting and emergency-comms training.

Conversion

Enter a starting year; the tool lists the next 5 leap years (Gregorian rule: divisible by 4 but, if divisible by 100, must also be divisible by 400), each with its distance in years from the start, plus the most recent prior leap year. Useful for project deadlines, birthday-on-Feb-29 planning and calendar trivia.

Date & Time

Enter odds in any one format and the tool returns the other three: European decimal (2.50), American (+150 / −200), British fractional (3 / 2) and the implied probability (40%). Essential conversion for sports betting, poker, value-betting and arbitrage analysis.

Finance

Enter the annual salary, days actually worked and the days-in-year basis (260 working days, 365 calendar days, etc.); the tool returns prorated_salary = annual_salary × days_worked ⁄ days_in_year. The standard formula HR uses for mid-year hires / leavers, unpaid leave and part-year contracts.

Finance

Enter two dates; the tool simultaneously reports the year fraction t under the four most-used day-count conventions (ACT/ACT, ACT/365 Fixed, ACT/360, 30/360 ISDA). Foundational for bond accrued interest, interest-rate swaps, annuities and insurance actuarial calculations.

Date & Time

Enter two points (or a slope plus a point); the tool returns all three canonical forms of the same line: slope-intercept y = mx + b, standard Ax + By = C (integer coefficients) and point-slope y − y₁ = m(x − x₁). The bread-and-butter conversion drilled in US Algebra I, SAT and SSAT.

Math

Enter (x, y) coordinates of three points; the tool computes the unique circumscribed circle's centre (h, k) and radius r, plus the standard-form equation (x − h)² + (y − k)² = r². Handy for geometry classes, CAD layouts, drafting and reverse-engineering arcs.

Math

Enter two people's birth dates; the tool returns the gap in years, months and days, plus the total day count and a percent comparison. Answers the most-Googled "how much older am I than my partner / sibling?" question.

Date & Time

Enter the semitone gap between two notes (or two frequencies directly); the tool returns the frequency ratio via 2^(n⁄12) and the cents gap via 1200·log₂(f₂⁄f₁). The standard tool for music theory, instrument tuning and harmonic analysis.

Lifestyle

Enter a distance (km, AU, light-years or parsecs); the tool uses c = 299 792 458 m/s to return the one-way light-travel time, with quick references for Earth–Moon, Earth–Sun and Earth–Mars distances. Useful for astronomy, deep-space communications and intro relativity classes.

Science

Enter the horizontal distance covered and the vertical altitude lost; the tool returns the glide ratio (L/D), the glide angle and the equivalent lift-to-drag ratio. The fundamental performance metric for paragliders, sailplanes, unpowered aircraft and skydivers.

Lifestyle

Enter wind speed in any unit (m/s, km/h, mph or knots); the tool maps it to Beaufort force 0–12 per the WMO standard, with the official sea-state and land-condition description. The international shorthand for sailors, hikers, aviators and outdoor sports.

Conversion

Enter one-way distance (km or mi), vehicle class (small / medium / large petrol, diesel, hybrid, PHEV, BEV, motorbike), passenger count and whether the trip is return-only or round-trip; the tool applies DEFRA 2024 well-to-wheel emission factors to return total vehicle CO₂, per-passenger share, annualised (× 250 commuting-day) emissions and a tree-month offset.

Science

Enter panel area, panel efficiency (%), average peak sun hours and the system performance ratio; the tool applies E = A × η × H × PR to return daily, monthly and annual kWh — the first sizing tool for any rooftop PV project.

Science

Enter the pre-money valuation, round size, new option-pool top-up % and your pre-round founder stake; the tool applies the standard VC pre-money pool convention to return post-money valuation, new-investor ownership, existing-shareholder share, the founder's post-round stake and the dual dilution (investor + pool). The cap-table sanity check for founders negotiating a term sheet.

Finance

Enter the project NPV (or initial cost), discount rate and life in years; the tool returns the Equivalent Annual Cost via EAC = NPV × r ⁄ (1 − (1 + r)⁻ⁿ), the annuity factor, the nominal total payments and the discount-free flat average for comparison. The standard capital-budgeting tool for comparing projects of different lifespans (e.g. a 5-year vs 8-year machine).

Finance

Enter dividends per share (DPS) and earnings per share (EPS) — or total dividends paid and net income — and the tool returns the payout ratio plus its complement, the retention ratio. The standard metric for gauging dividend sustainability and benchmarking blue-chip vs growth stocks.

Finance

Enter share price and revenue per share — or market cap and annual revenue — and the tool returns the P/S ratio with an industry-benchmarked band. The go-to valuation metric for high-growth or pre-profit companies (SaaS, biotech) where P/E breaks down.

Finance

Enter the catchment roof area, annual rainfall (mm) and surface runoff coefficient; the tool returns harvestable rainwater per year (litres / US gallons), monthly average and equivalent irrigation days. The first-pass sizing tool for residential rain barrels and garden irrigation systems.

Lifestyle

Enter the moles available for two reactants plus their stoichiometric coefficients from the balanced equation; the tool identifies the limiting reagent, returns the theoretical yield of product (mol) and the excess reagent remaining. The canonical homework calculation in A-level, AP and first-year university chemistry.

Science

Enter rotor diameter, wind speed, air density and the power coefficient Cp (Betz limit 0.593); the tool applies P = 0.5 × ρ × A × v³ × Cp to return instantaneous electrical power (kW), an annual-energy estimate and an equivalent number of households powered. The first-cut sizing tool for small wind turbines and off-grid systems.

Science

Enter accounts receivable, credit sales for the period and the number of days; the tool returns DSO = (AR ⁄ Credit Sales) × Days — the canonical metric for how quickly a company converts customer credit into cash. Core gauge of working-capital efficiency and liquidity.

Finance

Enter the loan principal and gross annual income; the tool returns LTI = Loan ÷ Gross Annual Income and benchmarks it against common regulatory caps (UK PRA 4.5×, Irish Central Bank 4×, equivalent HKMA stress-test DSR bands). The standard screen for mortgage affordability and leverage risk.

Finance

Enter altitude (and optionally sea-level pressure/temperature); the tool applies the ISA barometric formula p(h) = p₀ × (1 − Lh ⁄ T₀)^(gM ⁄ RL) to return ambient pressure in hPa, atm and psi. Standard reference for hiking, drones, mountaineering, aviation and cooking corrections at altitude.

Science

Enter any two of long-run arrival rate λ, time-in-system W, or average number in the system L; the tool returns the third via Little's Law L = λ × W — the foundational identity for queueing theory, WIP management in Agile/Kanban, and capacity planning for support desks and restaurants.

Math

Enter bandwidth and round-trip time (RTT); the tool returns BDP = Bandwidth × RTT (bits in flight) and converts to bytes and KB/MB. The fundamental sizing parameter for TCP socket buffers, congestion window targets and CDN prefetch tuning.

Math

Enter any three of initial pressure/volume and final pressure/volume of an isothermal gas; the tool returns the fourth via P₁V₁ = P₂V₂ — the foundational formula for scuba tank compression, syringes, engine pistons and air springs.

Science

Enter operating cash flow, capital expenditure and (optionally) the change in working capital; the tool returns Free Cash Flow = OCF − CapEx ± ΔWC and the FCF margin — the core input for DCF valuation, cash-on-cash return and margin-of-safety analysis.

Finance

Enter two strings; the tool returns the minimum number of single-character edits (insert / delete / substitute) needed to turn one into the other, plus a similarity percentage — the foundational algorithm for spellcheck, fuzzy matching, plagiarism detection and DNA sequence comparison.

Math

Enter solute concentration, temperature and the van 't Hoff factor i; the tool returns osmotic pressure via π = i·M·R·T — the foundational equation for cell osmosis, reverse-osmosis desalination membranes and isotonic IV fluid tonicity.

Science

Enter flour weight and water / salt / yeast / fat percentages (as % of flour weight); the tool returns each ingredient amount and the dough hydration using the standard baker's percentage system — the universal way bakers scale bread recipes up or down.

Lifestyle

Enter the focal length, f-number, and sensor circle-of-confusion; the tool returns the hyperfocal distance via H = f² ⁄ (N × c) + f — the defining number for landscape, street and astro photography focus-point selection.

Science

Enter total operating hours and number of failures; the tool returns MTBF = total hours ÷ failures, failure rate λ, and exponential reliability R(t) = e^(−t ⁄ MTBF) — the standard reliability-engineering metrics for hardware, servers and production lines.

Math

Enter wet-bulb, globe and dry-bulb temperatures; the tool returns WBGT via the ISO 7243 formula 0.7·Tnwb + 0.2·Tg + 0.1·Tdb and classifies the result against the NIOSH / US military flag system (white / green / yellow / red / black) — the international standard for assessing heat-stroke risk in sport and occupational settings.

Health

Enter R-value (thermal resistance) or U-value (thermal transmittance); the tool flips them via U = 1 ⁄ R and converts between SI (m²·K/W) and US (ft²·°F·h/BTU) units — the foundational conversion for roof, wall and window insulation specifications.

Conversion

Enter two equal-length strings or bit sequences; the tool compares them position by position and returns the Hamming distance (count of differing positions) — the foundational metric for error-correcting codes, DNA sequence comparison, hash similarity and coding theory.

Math

Enter the (x, y) vertex coordinates of a simple polygon (clockwise or counter-clockwise); the tool applies Gauss's shoelace formula A = ½|Σ(xᵢ·yᵢ₊₁ − xᵢ₊₁·yᵢ)| to return the enclosed area — used in surveying, cartography, GIS, CAD and game-development geometry.

Math

Enter up to 8 capacitances and pick series or parallel; the tool returns the equivalent capacitance via C_parallel = ΣCᵢ or 1⁄C_series = Σ(1⁄Cᵢ) — the basic tool for circuit design and filter calculations.

Science

Enter flow rate Q, total head H, fluid density and pump efficiency; the tool returns the required electrical power via P_shaft = ρ·g·Q·H ⁄ η in kW and HP — fundamental sizing equation for water supply, irrigation, fire-fighting and HVAC system design.

Science

Enter a grade and its source scale (US 4.0, Canadian 4.3, Indian 10-point, French 20-point, European percentage, etc.); the tool maps proportionally to every other scale and shows the equivalent letter grade — handy for international study applications and cross-institution grade comparisons.

Education

Enter lawn area, the NPK label numbers on the fertilizer bag (e.g. 10-10-10) and the target nitrogen rate (lb N per 1000 ft² or g N per m²); the tool returns how much fertilizer to apply and the actual N / P / K delivered — standard for lawn care, gardening and small-farm agronomy.

Lifestyle

Enter two points (x₁, y₁) and (x₂, y₂); the tool instantly returns the midpoint M = ((x₁+x₂)⁄2, (y₁+y₂)⁄2), the Euclidean distance d = √((Δx)² + (Δy)²) and the slope m = Δy⁄Δx — handy for geometry homework, surveying, GIS and CAD work.

Math

A basis point (bp) is the standard unit for small changes in financial rates — 1 bp = 0.01 %, 100 bp = 1 %. Enter bps or % and the tool converts both ways, with optional application to a notional principal, rate or bond spread — eliminates the ambiguity behind "Fed hikes 25 bps" headlines.

Finance

Enter the asset cost, salvage value and useful life; the tool builds a year-by-year double-declining balance (DDB) schedule with depreciation expense, accumulated depreciation and book value — an accelerated method permitted by US GAAP and IFRS, widely used for vehicles, computers and machinery whose value drops sharply in the early years.

Finance

Enter a currency pair, lot size, quote price and account currency; the tool returns the cash value of one pip (and one pipette) for that trade — essential for MT4 / MT5 traders, forex risk management and stop-loss / take-profit placement.

Finance

Enter a paper weight in either GSM (metric grammage) or US-system pounds (bond, cover, text, index or tag) and the tool converts in both directions via the basis-weight ratio, plus shows typical use cases (copy paper, business cards, posters, magazine covers) — handy for print buying, design specs and comparing imported paper stock.

Conversion

Continuous compounding is the limit of more-frequent periodic compounding: A = P·e^(rt). Enter principal, rate and time; the tool returns the final amount and total interest, and contrasts it with finite-period compounding (monthly / quarterly / semi-annual / annual) — used in options pricing, Black-Scholes and academic finance.

Finance

Slope can be expressed three ways: percent grade (rise⁄run × 100 %), degrees (arctan(rise⁄run)) or ratio (1:N). Enter any one and the tool instantly converts to the other two — useful for hiking, cycling, road signs, accessibility ramps and roof pitch.

Conversion

Current yield = annual coupon ÷ current market price — the simplest measure of a bond's instant cash return. Enter par value, coupon rate (or coupon $) and market price; the tool returns current yield and contrasts it with the coupon rate — a quick first look at bonds trading at premiums or discounts.

Finance

Heat pump COP = heat output Q ÷ electrical work input W. Enter the heat delivered and electricity used; the tool returns the COP and contrasts it with the Carnot upper bound COP_max = T_hot ⁄ (T_hot − T_cold) — useful for sizing AC, heat pumps, underfloor heating and water heaters.

Science

Enter the edge length a of a regular tetrahedron; the tool returns volume V = a³ ⁄ (6√2), total surface area A = √3·a², height h = a·√(2⁄3) and the inscribed / circumscribed sphere radii — handy for crystallography, molecular geometry (methane CH₄), organic chemistry and pure geometry problems.

Math

Enter the larger radius R, smaller radius r and height h of a cone frustum; the tool returns volume V = πh(R² + Rr + r²) / 3, slant height ℓ, lateral surface area, the two circular faces and total surface area — useful for paper cups, lampshades, funnels and water tanks.

Math

The Sabine formula RT60 = 0.161·V / A (metric) estimates the time it takes for sound to decay 60 dB inside a room. Enter the room volume and the total effective absorption (Σ Sᵢ·αᵢ); the tool returns RT60 and compares it against recommended ranges for studios, classrooms and concert halls.

Science

Enter your straight ladder length and the height where it touches the wall; the tool returns the required base distance from the wall, the angle with the ground, and checks them against the OSHA / EN 131 "4-to-1" rule (1 unit of base for every 4 units of working height, ≈ 75.5°) — handy for home maintenance, painting and window cleaning.

Lifestyle

Enter a score from any one of the three big English tests (IELTS 0–9, TOEFL iBT 0–120, Duolingo DET 10–160); the tool converts to the other two using the official / industry-recognised concordance tables — useful for study-abroad applications, CEFR level mapping and cross-test comparison.

Education

Enter the radicand x and the root index n; the tool returns the real nth root x^(1/n), handling negative x with odd n, fractional roots and complex-only cases with a clear warning — for cube roots, fifth roots, principal roots and inverse-power problems.

Math

Enter a blood glucose value; the tool converts between mg/dL and mmol/L — the two globally-used units (mg/dL in the US, mmol/L in Europe, China, Hong Kong and elsewhere). Essential when reading lab reports across borders.

Conversion

Enter your HbA1c value; the tool converts between NGSP units (%) and IFCC units (mmol/mol) — both are used in clinical practice worldwide, and diabetes monitoring requires reading reports in the right unit.

Conversion

Enter total cholesterol, LDL, HDL or triglycerides; the tool converts between mg/dL and mmol/L using the standard conversion factors (38.67 for cholesterol classes, 88.57 for triglycerides) — useful when reading US-style and European-style lipid panels.

Conversion

Enter a digit string; the tool validates it with the Luhn (mod-10 doubling) algorithm and computes the trailing check digit that makes the first N − 1 digits valid — the same scheme used by credit cards (Visa, Mastercard, Amex), phone IMEIs and Canadian SINs.

Math

Enter an ISBN-13 (with or without the trailing digit); the tool computes the correct check digit using the (1, 3) weighted mod-10 formula and validates the entire string — useful for librarians, publishers and bookshops managing catalogues.

Math

Enter the standard cell potential E°, number of electrons transferred n, reaction quotient Q and temperature; the tool returns the actual cell potential via the Nernst equation E = E° − (RT/nF) ln Q — used in electrochemistry, battery design, corrosion analysis and nerve-membrane potentials.

Science

Enter a gas concentration (ppm or mg/m³), molecular weight, temperature and pressure; the tool converts in both directions via the ideal-gas law — used in indoor air quality, occupational safety (OSHA / NIOSH PELs) and environmental monitoring.

Conversion

Enter solute mass / volume and total solution mass / volume; the tool returns mass percent (% w/w), mass-volume percent (% w/v) and volume percent (% v/v) — standard in chemistry class, food labelling and pharmaceutical formulation.

Science

Paste English text; the tool computes the Coleman-Liau Index (based on letter count and sentence count) to estimate US grade reading level — unlike Flesch-Kincaid, it needs no syllable counting and is easier to automate.

Education

Enter cadence (steps per minute) and stride length (cm or m); the tool returns running speed (km/h, mph), pace (min/km, min/mi) and distance per minute — handy for runners on Garmin, Apple Watch and Strava tuning cadence vs stride.

Health

Enter current temperature, current tire gauge pressure and target / future temperature; the tool returns the adjusted gauge pressure via Gay-Lussac's gas law — useful for winter inflation, long-distance driving and bicycle pressure under temperature swings.

Lifestyle

Enter any positive integer; the tool repeatedly sums its digits until a single digit remains — showing each iteration, the numerology life-path equivalent and the mod-9 identity.

Math

Enter initial pressure, volume, temperature and the heat-capacity ratio γ; the tool applies the isentropic relations PVγ = const and TVγ−1 = const to give the new P, V and T — standard for internal-combustion engines, compressors and rocket nozzles.

Science

Enter diopters (D) or focal length (mm / m / inch); the tool converts both ways via P = 1 / f(m) — used for eyeglass prescriptions, myopia / presbyopia correction, close-up filters and magnifier ratings.

Conversion

Enter water weight and target salt % by weight to get grams of salt — or back-compute the % from existing salt + water. Common in pickling, lacto-fermentation, sous-vide brining; includes the standard 2 % / 3.5 % / 5 % recipe reference table.

Lifestyle

Enter the tank or pool volume (L, m³, gal) and the inflow rate (L/min, GPM, m³/h …); the tool gives the fill time. Useful for pools, ponds, aquariums and water tanks.

Lifestyle

Enter air temperature and relative humidity (and optionally leaf temperature); the tool applies the Tetens saturation-vapor-pressure formula to return the vapor pressure deficit in kPa — the single most-used environmental metric for indoor hydroponics, commercial greenhouses, cigar humidors and fruit ripening rooms.

Science

Enter the diameters of the two pulleys and the center-to-center distance; the tool returns the V-belt length via the standard closed-form L = 2C + π(D₁ + D₂)/2 + (D₁ − D₂)² / (4C) and shows the wrap angles on each pulley. Useful for industrial fans, lathes and any open belt drive.

Science

Enter spot price, strike, time to expiry, risk-free rate, volatility and optional dividend yield; the tool applies the Black-Scholes-Merton 1973 model to return the European call and put prices, d₁ / d₂ and the full set of Greeks (Delta, Gamma, Vega, Theta, Rho) — the standard reference for option pricing, sanity-checking quotes and exploring implied volatility.

Finance

Enter field elevation, QNH altimeter setting and OAT; the tool applies the standard FAA Pilot's Handbook formula and reports pressure altitude (PA), the ISA standard temperature, the deviation from ISA and the density altitude (DA) — essential for takeoff performance, high-altitude training and drone lift planning.

Science

Enter cumulative sales and 1–5 tiered commission rates (e.g. 5 % on the first 100 k, 6 % on the next, 8 % above) and the tool returns total commission, marginal and effective rates, plus the contribution of each tier — used by sales reps, sales managers and year-end payroll.

Finance

Enter the A-weighted sound level (dBA); the tool returns the maximum daily safe exposure time using both the NIOSH (3 dB exchange) and OSHA (5 dB exchange) rules — relevant to concerts, construction sites, headphone listening and factory floors. Includes a reference table of common noise levels.

Lifestyle

Enter carrying capacity K, initial value N₀, intrinsic growth rate r and time t; the tool applies the Verhulst logistic equation N(t) = K / (1 + ((K−N₀)/N₀)·e^(−rt)) and reports current value, instantaneous growth rate and half-saturation time — universal model for population dynamics, epidemic spread, start-up adoption curves and any growth limited by a carrying capacity.

Math

Enter a duration in any unit (seconds, minutes, hours, days, weeks, months, years, decades, centuries, millennia) and the tool converts to every other unit simultaneously — using year = 365.25 days (IAU Julian) and month = 30.4375 days.

Conversion

Enter average order value, purchase frequency, gross margin, churn (or expected lifetime) and discount rate; the tool applies the steady-state formula CLV = (AOV × Freq × Margin) / (Churn + Discount) to give the net present value of one customer over their entire relationship — the standard SaaS, subscription, retail and e-commerce metric.

Finance

Enter focal length, aperture, focus distance and sensor format; the tool returns the hyperfocal distance, near-limit, far-limit and total depth of field — the core tool landscape, product and portrait photographers use to plan how much of a scene will be acceptably sharp.

Science

Paste the high, low and close for the last N bars; the tool applies Wilder's True Range max(H − L, |H − C_prev|, |L − C_prev|) and his RMA smoothing to give ATR — the standard volatility measure for sizing futures, FX and crypto stops and positions.

Finance

Enter a 2×2 matrix [[a, b], [c, d]]; the tool applies the closed-form A⁻¹ = 1/det(A) × [[d, −b], [−c, a]] to return the inverse together with the determinant (det = ad − bc) — and reports "singular" when det = 0.

Math

Enter the installation latitude; the tool applies the standard NREL Landau / Heliene rules to give the year-round optimal fixed tilt, the summer tilt and the winter tilt — the headline number every rooftop PV, off-grid system and solar-thermal installer sizes by.

Science

Enter any two of frequency f, wavelength λ and wave speed v; the tool applies v = f × λ to return the third together with the period T, angular frequency ω and angular wavenumber k. Built-in presets cover sound in air, fresh water, sea water and steel, plus EM in vacuum, water and glass — the most basic wave relation used across acoustics, radio, optics and ocean waves.

Science

Enter two points (x₁, y₁) and (x₂, y₂) — with optional z to extend to 3D — and the tool applies M = ((x₁ + x₂)/2, (y₁ + y₂)/2) to give the midpoint, the Euclidean distance and the slope (in 2D). Used in high-school coordinate geometry, CAD drafting and game-coordinate math.

Math

Enter starting shares, share price, annual dividend yield (DPS / price), expected annual price growth and horizon; the tool runs the year-by-year compounding loop — each dividend is fully reinvested into new shares, which earn the next round of dividends — and reports the final share count, market value, cumulative dividends and annualised CAGR. The standard analysis tool for long-term dividend reinvestment in stocks such as SPY, AAPL and KO.

Finance

Enter buy price, sell price, total cash received during the holding period (dividends / coupons / distributions) and the length of the period; the tool computes the holding-period return (HPR) and the annualised HPR — works for stocks, bonds, ETFs and funds and shows the complete picture of capital gain plus cash distributions.

Finance

Enter hot-side inlet and outlet temperatures, cold-side inlet and outlet temperatures, and pick counter-flow or parallel-flow; the tool applies LMTD = (ΔT₁ − ΔT₂) / ln(ΔT₁ / ΔT₂) to give the log mean temperature difference — the fundamental quantity in shell-and-tube, plate, AC-condenser and chemical-process heat-exchanger sizing.

Science

Pick a solid shape (sphere, cube, cylinder, cone) and enter its dimensions; the tool returns the surface area (sphere 4πr², cube 6a², cylinder 2πr² + 2πrh, cone πr² + πrl) and the volume — useful for estimating paint, packaging, wrap film and insulation requirements.

Math

Enter the number of defects and total opportunities — or DPMO directly — and the tool returns the yield (1 − DPMO / 10⁶), the long-term sigma level (without shift) and the short-term Six Sigma level (with the conventional 1.5 σ shift) — the standard Motorola / Lean Six Sigma process-capability score.

Math

Enter the torus major radius R (centre of ring to centre of tube) and the tube radius r; the tool applies V = 2π²Rr² and SA = 4π²Rr to give the volume and surface area of the torus (donut shape) — useful for pipe elbows, rubber O-rings, inner tubes and magnetic ring cores.

Math

Enter the lamp wattage W and luminous efficacy (lm / W) — or known lumens and efficacy — and the tool uses lm = W × η to convert between input power and light output, with built-in reference efficacies for incandescent, halogen, CFL and LED bulbs — essential when picking the right LED brightness to replace an old wattage bulb.

Conversion

Enter the seconds between seeing the flash and hearing the thunder; the tool uses the speed of sound (≈ 343 m/s, light arrives essentially instantly) to compute distance in km and miles, with NOAA "30/30 rule" guidance on when to seek shelter.

Science

Enter the balloon diameter and the payload weight; the tool applies lift ≈ (ρ_air − ρ_He) × V to give the net lift per balloon (≈ 1 g per litre at sea level), how many balloons you need, and notes on envelope weight and altitude density effects.

Science

Enter antenna gain in dBi (or as a linear ratio); the tool applies G = 10^(dBi/10) to convert between dBi and ratio, with reference ranges for common antenna types (whip, Yagi, parabolic, patch, WiFi router) — essential for picking WiFi, two-way radio or satellite antennas.

Science

Enter skid mark length and road surface friction coefficient μ; the tool applies v = √(2μgd) to estimate the minimum entry speed when braking began (km/h and mph) — used in crash reconstruction, insurance assessment and driving safety analysis.

Science

Enter the finished concrete volume and the cement : sand : coarse-aggregate mix ratio (e.g. the classic 1:2:3); the tool returns each material in kg, m³ and bag count, applying the standard 1.54 dry-to-wet bulking factor — essential for DIY slabs, planters and footings.

Lifestyle

Pick gender (men / women) and garment type (tops / bottoms), enter any region size; the tool instantly returns the matching US, UK, EU and JP sizes alongside the standard bust / chest / waist range — essential for online shopping, travel and overseas purchases.

Conversion

Enter the karat (24K = pure), percent purity, or millesimal fineness (999 = pure); the tool simultaneously shows all three values and the international hallmark grade it corresponds to (e.g. 750, 585, 375) — useful for buying jewellery, scrap-gold valuation and customs checks.

Conversion

Enter aperture f-number, shutter time and ISO; the tool returns EV = log₂(N²/t) − log₂(ISO/100), maps it to a typical scene (sunny day, indoor, moonlight) and lists five equivalent-exposure pairs (same EV, different aperture / shutter combinations) — handy for Sunny-16, night and moonlight photography.

Science

Enter a frame rate (24 / 25 / 29.97 / 30 / 60 / 120 fps or custom) and clip duration; the tool reports frame duration (ms), total frames, and cross-references industry standards — film, PAL, NTSC, web, high-speed — useful for post-production, animation timing and game-engine work.

Conversion

Enter image width, height, colour mode (grayscale / RGB / RGBA / CMYK) and bit depth (8 / 10 / 12 / 16 bit); the tool returns the uncompressed raw size and estimates for high-quality JPEG, standard JPEG, low-quality JPEG and lossless PNG.

Conversion

Enter sample rate (Hz), bit depth (8 / 16 / 24 / 32 bit), channel count (mono / stereo / 5.1 / 7.1 / Atmos) and duration; the tool instantly returns the Nyquist limit, raw PCM bitrate, bytes-per-second and the uncompressed WAV file size.

Science

Enter height and wrist circumference; the tool applies Grant's index r = height ÷ wrist circumference to classify body frame (small / medium / large) — used to adjust "ideal weight" estimates and reflects bone-structure differences that a single BMI value cannot.

Health

Enter the four coefficients of ax³ + bx² + cx + d = 0; the tool applies the Cardano-Tartaglia formula to return all three roots (real or conjugate-complex), the discriminant Δ and the type of root configuration.

Math

Enter assets (cash, investments, property, vehicles, other) and liabilities (mortgage, credit cards, student loans, car loans, other); the tool returns total assets, total liabilities and net worth, plus the debt-to-asset ratio (DTA) and liquid-to-debt ratio commonly used to gauge financial health.

Finance

Enter latitude (° N or S); the tool applies v = (2π · R · cos φ) ÷ T (where R is Earth's equatorial radius and T = 86 164 s, one sidereal day) to compute the linear speed of the ground at that latitude in m/s, km/h and mph — explains why equatorial launch sites (Cape Canaveral, Kourou) get a "free kick" for rocket launches.

Science

Enter initial volume V₁, initial temperature T₁ and final temperature T₂ (in °C or K); the tool applies Charles's Law V₁/T₁ = V₂/T₂ (at constant pressure) to find the final volume V₂. Any one variable can be left blank to solve for it.

Science

Enter water hardness in any unit (gpg, ppm/mg-L CaCO₃, mmol/L, German degrees °dH, French °fH, English °eH); the tool converts to all other units at once and classifies the water as soft, moderately hard, hard or very hard.

Conversion

Enter inseam (the floor-to-crotch length); the tool returns the recommended saddle height using LeMond's formula (inseam × 0.883, bottom-bracket to top-of-saddle) and the Hamley/Holmes method (~109% inseam to pedal), together with the 25°–35° knee-angle range for reference.

Health

Enter snow depth (cm or inches) and snow density (kg/m³, or pick a preset for fresh / powder / wet / packed snow); the tool returns the equivalent water-column height after melting (mm or inches) and the mass per square metre (kg) — used for avalanche risk, roof load and irrigation water supply.

Science

Enter total pages, current page and a deadline; the tool returns pages-per-day required and projected finish date. Can also invert: how many days to finish at X pages per day.

Education

Enter treadmill speed (km/h or mph) and incline (%); the tool uses the ACSM running metabolic equation to return the equivalent flat-ground pace (min/km and min/mile) so you can compare indoor and outdoor effort.

Health

Two modes: (1) compute μ = F/N from friction force F and normal force N; (2) compute static coefficient μ_s = tan θ from the incline angle θ at which an object just starts to slip. A staple of physics labs and engineering classes.

Science

Enter density in any unit; the tool converts to kg/m³, g/cm³ (= g/mL), lb/ft³, lb/US gal, lb/UK gal and kg/L at once — useful in engineering design, chemistry labs and shipping payload calculations.

Conversion

Enter Young's modulus E, cross-section (solid round / rectangle / pipe), length L and an effective-length factor K (0.5 fixed-fixed, 0.7 fixed-pinned, 1.0 pinned-pinned, 2.0 fixed-free); the tool computes the minimum moment of inertia, radius of gyration, slenderness ratio and the critical buckling load P_cr — the foundation tool for slender-column stability design.

Science

Enter the price and pack size of two products (mix units freely — g / kg / mL / L / pcs); the tool computes price-per-unit, flags the cheaper option, shows percentage savings and a normalised per-100 g / per-100 mL comparison.

Lifestyle

Enter a volumetric flow rate in any unit (L/s, L/min, m³/h, US gpm, UK gpm, ft³/s (cfs), ft³/min (cfm), etc.); the tool converts to all the other common units at once — handy for pumps, HVAC, fire-protection and irrigation work.

Conversion

Pick a fasting protocol (14/10, 16/8, 18/6, 20/4, OMAD, etc.) and your last-meal time; the tool returns when you can break the fast next, tomorrow's eating-window start and end, and total weekly fasting hours — useful for planning an IF schedule.

Health

Enter the target word count and your effective writing rate (words/minute), optionally with a revision-and-proofread multiplier; the tool estimates total writing time and the words-per-day pace needed to finish before a chosen deadline.

Education

Enter multiple value + weight pairs; the tool returns the weighted mean Σ(xᵢwᵢ) ⁄ Σwᵢ — unlike a simple arithmetic mean, heavier-weighted entries count more. Common uses: course grades, portfolio returns, survey scores.

Math

Enter your target hours per night plus the actual hours slept each of the past 7 nights; the tool returns total accumulated sleep debt (hours), average nightly shortfall, and how many consecutive "+1 h" nights are needed to clear it.

Health

Enter your target barbell total weight, the empty bar weight and the plates available in your gym (kg or lb); the tool uses a greedy decomposition to list the plates per side and flags any remainder that can't be matched.

Lifestyle

Enter the vertical rise and horizontal run of a roof slope; the tool returns the pitch as a percent, degrees, the North-American X-in-12 ratio, and the rafter (hypotenuse) length via the Pythagorean theorem.

Lifestyle

Enter the cutter diameter and recommended surface speed (SFM or m/min); the tool applies RPM = (SFM × 12) ⁄ (π × D) to give the spindle speed — the standard machinist conversion used for drills, end mills and lathes.

Science

Enter filament diameter (1.75 mm or 2.85 mm), length in metres and material (PLA / PETG / ABS / TPU / Nylon / PC — density auto-fills); the tool applies m = π·(d/2)²·L·ρ to give the mass in grams, and inverts to answer "how many metres on a 1 kg spool".

Science

Enter roof snow depth (cm or in) and snow type (fresh 50 kg/m³, settled 200, wet 400, ice 917); the tool computes the surface load in kPa, psf and kg/m² so you can compare to local building codes (IBC, NBC, Eurocode 1).

Science

Enter the tank water volume (litres / US or imperial gallons), target water temperature and the coldest expected room temperature; the tool uses W ≈ 0.25 × V_L × ΔT (matching the Eheim Jager / Marina / Hagen sizing charts) to suggest a wattage, the closest commercial heater size and when to split into two heaters.

Lifestyle

Enter the food thickness (mm), shape (slab / cylinder / sphere), type and bath / initial temperature; the tool applies Baldwin's heat-diffusion equations to estimate the time for the core to reach the bath (within 0.5 °C, the Baldwin standard) — sous-vide time depends on thickness, not weight.

Lifestyle

Enter the vertical rise; the tool applies the widely-adopted 1:12 maximum slope (US ADA, ISO 21542, UK Approved Doc M, Singapore BCA) to give the minimum ramp length, and lists the per-9 m landing rule, handrail requirements and other code-compliance checks.

Lifestyle

Enter an upper bound N for the hypotenuse c; the tool uses Euclid's formula a = m²−n², b = 2mn, c = m²+n² to enumerate every primitive Pythagorean triple (gcd(a,b,c) = 1) up to that bound, with an option to list non-primitive multiples too.

Math

Enter the radius r and height h of a cylinder; the tool returns the total surface area (two circular caps + lateral surface), the lateral surface alone, and a single cap, expressed in cm², m², in² and ft².

Math

Enter the length, width and depth of a raised garden bed (cm or in); the tool returns the soil volume needed in litres, cubic feet and cubic yards, and converts that into the number of bags at common retail sizes (20 L, 40 L, 50 L, 1.5 cu ft, 2 cu ft) so you can buy the right amount from the garden centre.

Lifestyle

Enter daily high and low temperatures and a crop base temperature (corn 10 °C, wheat 4 °C, cotton 15 °C, etc.); the tool applies the standard ((Tmax + Tmin) ⁄ 2) − Tbase formula to give the day's GDD and a running cumulative total — used by growers, gardeners and IPM scouts to predict bloom, harvest and pest emergence windows.

Science

Enter outer radius R and inner radius r; the tool returns the annular area, the outer disk area, the inner hole area and the ring width in mm², cm², m², in² and ft² — useful for washers, gaskets, running tracks and tree-ring growth.

Math

Enter your Earth age; the tool uses each planet's orbital period around the Sun (Mercury 87.97 d, Venus 224.7 d, Mars 686.97 d, Jupiter 11.86 yr…) to compute your equivalent age on each of the other seven planets plus Pluto.

Science

Enter the annual pre-tax cash flow from a property or investment and the actual cash you invested (down payment plus closing costs); the tool returns CoC = annual_cash_flow ⁄ total_cash_invested — real-estate investors' standard benchmark for cash-on-cash efficiency.

Finance

Enter your age; the tool reports the recommended sleep range from the US National Sleep Foundation's 2015 consensus guidelines (newborns 14–17 h, infants 12–15 h, preschoolers 10–13 h, adults 7–9 h, older adults 7–8 h) and a suggested bed-and-wake schedule.

Health

Enter water volume (litres), starting temperature and the kettle wattage; the tool applies Q = m·c·ΔT to give the energy (kJ / Wh) and time needed to reach 100 °C (or a custom target) and also reports the latent heat needed to fully evaporate.

Science

Enter annual mileage, fuel economy, insurance, maintenance, depreciation, parking and loan interest; the tool returns the true cost per mile (and per km) so you can compare owning a car to ride-share, public transit or short-term rental.

Lifestyle

Enter your height and a target BMI (e.g. 22.0); the tool computes the matching weight from W = BMI × (height/100)² in both kg and lb, plus how much you need to gain or lose from your current weight.

Health

Enter the car price, down payment, annual interest rate and loan term; the tool applies the standard amortization formula to give the monthly payment, total interest, total repayment, and a 12-month principal/interest split.

Finance

Enter tank volume (litres / gallons), incoming and target water temperature, heater rated power (W or BTU/h) and efficiency; the tool applies Q = m·c·ΔT to give the time needed to bring a full tank up to temperature.

Science

Enter the average daily demand, demand standard deviation, lead time and target service level; the tool applies Safety Stock = Z × σ_d × √L and ROP = d̄ × L + SS to give the reorder point that meets your stock-out tolerance.

Finance

Enter the initial and final principal quantum numbers n₁ and n₂; the tool applies E_n = −13.6/n² eV and the Rydberg formula 1/λ = R(1/n₁² − 1/n₂²) to give the energy levels, transition energy, photon wavelength and frequency (Lyman / Balmer / Paschen series).

Science

Enter the transmit frequency (MHz / GHz) and the distance (m / km / mi); the tool applies the Friis free-space path loss formula FSPL(dB) = 20·log₁₀(d) + 20·log₁₀(f) + K, useful for Wi-Fi, LoRa, 4G/5G and satellite link-budget estimates.

Science

Enter the bed length × width (m or ft), the in-row spacing and the row spacing; the tool computes the number of plants for both square-grid and triangular (offset) layouts plus the effective planting area — handy before ordering seedlings or seeds.

Lifestyle

Enter the battery system voltage (12 / 24 / 48 V), chemistry (LiFePO₄, Li-Ion NMC, lead-acid / AGM) and measured open-circuit voltage; the tool linear-interpolates the standard rest-voltage SoC table to give the percent state of charge, remaining headroom to low-voltage cut-off, and warns when you are at the floor.

Science

Enter the roast type (beef, pork, lamb, chicken, turkey), weight (kg or lb), desired doneness (rare/medium/well) and oven temperature; the tool consults the USDA / British Beef & Lamb published "minutes-per-pound" tables to give the suggested cooking time, plus pre-heat, rest and core-temperature guidance.

Lifestyle

Enter rider + bike weight, speed, gradient (%), aerodynamic CdA, rolling resistance Crr and headwind; the tool sums the three drag components (gravity, aero, rolling) to give the power (watts) needed to hold that speed — useful for FTP comparison, climb pacing and gear-upgrade decisions.

Lifestyle

Enter the two parental genotypes (e.g. Aa × Aa); the tool draws the 2×2 Punnett square and reports the offspring genotype and phenotype ratios.

Math

Enter the pool volume (L or US gal), current free-chlorine ppm and target ppm; the tool returns the dose of liquid sodium hypochlorite (bleach) or calcium hypochlorite (trichlor) needed.

Lifestyle

Enter the cap cost, residual value, term, money factor and down payment; the tool applies the industry-standard lease formula to split the monthly bill into depreciation, finance charge and pre-tax total.

Finance

Enter the recessive-phenotype frequency q² (or the dominant allele frequency p); the tool applies p + q = 1 and p² + 2pq + q² = 1 to back out the expected fractions of homozygous-dominant, heterozygous and homozygous-recessive genotypes, plus carrier frequency among the unaffected.

Math

Enter the loan principal, annual rate, scheduled monthly payment and the extra you can pay each month; the tool runs month-by-month amortisation to show the time and interest saved, and compares the with- vs without-extra payoff timelines.

Finance

Enter the surface air temperature and dew point; the tool applies the standard aviation approximation 125 m per °C of dew-point spread to estimate the cumulus cloud base (lifting condensation level, LCL).

Science

Enter the lens focal length (mm) and sensor size (full-frame, APS-C, M4/3, 1-inch, etc.); the tool returns the horizontal, vertical and diagonal angle of view in degrees — useful for lens choice, framing estimates and landscape / portrait planning.

Science

Enter the supply voltage, the LED forward voltage (per colour, per series count) and the target current (mA); the tool applies Ohm's law to give the limiting resistor value (Ω), the minimum wattage and the closest standard E12 value.

Science

Enter the native focal length and the sensor format (full-frame 1.0×, APS-C 1.5/1.6×, M4/3 2.0×, 1-inch 2.7×, etc.); the tool returns the 35 mm-equivalent focal length and the depth-of-field-equivalent aperture, making cross-system lens comparisons straightforward.

Science

Enter a conventional oven temperature (°C or °F) and time; the tool applies the standard fan-oven rules (drop ~20 °C / 25 °F, multiply time by ~0.80) to give the convection setting — and works in reverse, too.

Lifestyle

Enter each ingredient (spirits, liqueurs, syrup, juice, water) by volume (mL) and ABV (%); the tool adds the standard stir or shake dilution and returns the finished drink's total volume, final ABV and the number of standard drinks.

Lifestyle

Enter the carbohydrate grams in a meal, pre- and post-meal glucose, the rapid-acting insulin units used and the glucose target; the tool applies the 500/TDD rule with the insulin sensitivity factor (ISF) to give a personalised ICR (g of carb per 1 U of insulin) and a suggested bolus.

Health

Enter the wall length × height, brick size (UK standard 215 × 102.5 × 65 mm, metric 240 × 115 × 71 mm or custom), mortar joint thickness (mm), the area of openings to subtract and a wastage factor; the tool returns the total bricks needed, mortar volume (m³) and a recommended safety surplus.

Lifestyle

Enter the span L, Young's modulus E, second moment of area I and the load type (centre point P or uniformly distributed w) for a simply supported beam; the tool applies δ = PL³/(48EI) or δ = 5wL⁴/(384EI) to give the mid-span deflection and maximum bending moment — a quick sanity check for woodworking, civil and mechanical work.

Science

Enter the fridge's rated wattage (W) or the nameplate kWh/year, the actual duty cycle (compressor-on fraction, typically 30–50 %) and your electricity tariff; the tool returns the yearly kWh, cost and CO₂ emissions — useful for comparing replacement models against your current one.

Lifestyle

Enter the current (A), allowable temperature rise ΔT (°C), copper weight (oz/ft², typically 0.5 / 1 / 2) and whether the trace is on an external or internal layer; the tool applies the IPC-2221 formula I = k·ΔT^0.44·A^0.725 to give the required trace width (mm / mil) — a quick PCB layout sanity check.

Science

Enter the total running time (hh:mm:ss) and distance (km or mile); the tool returns pace per kilometre, pace per mile, average speed (km/h, mph) and per-km / per-mile split tables — a quick way to compare training and race performance.

Health

Enter a note name (C, C♯, D … ) and octave (e.g. A4, C5); the tool applies the 12-tone equal-temperament formula f = 440 × 2^((n − 69)/12) to give the frequency (Hz). Reverse mode: enter a Hz value and the tool reports the nearest note and cents deviation — useful for tuning, synth design and acoustics work.

Science

Enter the wall length (ft or m) and the on-centre stud spacing (16 in, 19.2 in, 24 in or custom); the tool returns the required stud count including end studs, extra king / jack studs at openings, plus the total linear footage / metres of lumber for budgeting and ordering.

Lifestyle

Pick a tea type (green, white, oolong, black, pu-erh, herbal, Earl Grey, matcha, etc.) and the tool shows the recommended water temperature range (°C / °F), first-steep time (seconds), number of re-steeps and per-steep extension — a handy reference for café training and home brewing.

Lifestyle

Enter the pedalling cadence (RPM), front / rear sprocket teeth (chainring / cog) and wheel size (700×25c, 26 inch, etc.); the tool applies speed = cadence × (chainring / cog) × wheel_circumference to give distance per minute (m/min), km/h, mph and the gain ratio per pedal stroke — useful for picking a gear and pacing training rides.

Lifestyle

Enter the VSWR (voltage standing-wave ratio) or the return loss in dB; the tool applies Γ = (VSWR − 1)/(VSWR + 1) and RL = −20·log₁₀|Γ| in both directions, and reports the reflected/transmitted power percentages — a quick sanity check for antenna, RF and transmission-line work.

Science

Enter the telescope aperture (mm), main focal length, eyepiece focal length and Barlow factor; the tool returns magnification M = f_tel × Barlow ÷ f_eye, exit-pupil diameter (D ÷ M), focal ratio, maximum useful magnification (~ 2 × aperture mm), minimum useful power (~ aperture ÷ 7 mm dark-adapted) and the Dawes / Rayleigh diffraction limits — the numbers that decide whether an eyepiece (or planned purchase) is the right match.

Science

Enter the lawn area, mower cutting width, walking/driving speed and pass overlap; the tool returns the pure mowing time plus a turning and setup buffer — useful for weekend yard planning or quoting a landscaping job.

Lifestyle

Enter the largest chainring, largest rear sprocket and chainstay length; the tool applies the Park Tool formula L = 2·C + (F/4 + R/4 + 1) to give the required chain length in inches and links — useful for replacing the drivetrain, swapping a cassette or sizing a new chain after a break.

Lifestyle

Enter the string length (mm), tension (N) and linear mass density (g/m); the tool applies f₁ = (1/2L)·√(T/μ) to give the fundamental and the first 8 harmonics — useful for guitar, violin or piano string tuning and for classroom demonstrations of standing waves.

Science

Enter the cylinder bore (mm), stroke (mm) and cylinder count; the tool applies V = π · (bore/2)² · stroke · cylinders to give engine displacement in cc, L and cubic inches — useful for motorcycles, car tuning and mechanical-engineering teaching.

Science

Enter the driver pulley diameter, driven pulley diameter and input RPM; the tool applies RPM_out = RPM_in × (D_drive / D_driven) to give output RPM, reduction ratio and belt linear speed (m/s) — useful for mechanical, agricultural and CNC retrofits.

Science

Enter the target score, current score, overs bowled and total overs; the tool returns the required run rate (RRR), current run rate (CRR), balls remaining and runs-per-ball needed — useful for cricket fans tracking a chase.

Math

Enter the hub flange radius, flange spacing, rim ERD and cross pattern; the tool applies L = √(d² + r² + R² − 2·r·R·cos(α)) − D/2 to give the spoke length per side — useful for DIY wheel-building and spoke purchasing.

Lifestyle

Enter the pitcher's earned runs (ER) and innings pitched (IP); the tool applies ERA = (ER × 9) / IP to give the normalised "earned runs per nine innings" — the universal pitching benchmark used by MLB, NPB, KBO, CPBL and the WBSC.

Math

Enter the runway heading (°T), wind direction and wind speed (kt or m/s); the tool applies crosswind = V·|sin α| and headwind = V·cos α to give orthogonal components — used by pilots, gliders and UAV operators to assess take-off and landing risk.

Science

Enter the pin counts for all ten frames; the tool applies World Bowling / USBC rules for strike (X) and spare (/) bonuses, including the tenth-frame fill balls, and gives the running per-frame total and final score.

Math

Enter vehicle power (hp) and total weight (lb or kg); the tool applies Hale's empirical formulas ET = 5.825 × (W/HP)^(1/3) and trap-speed = 234 × (HP/W)^(1/3) to estimate the 1/4-mile elapsed time and terminal speed — a drag-strip rule-of-thumb.

Science

Enter the waterline length (LWL, ft or m); the tool applies the Froude-derived hull_speed = 1.34 × √LWL (kn) to estimate the theoretical top speed of a displacement hull — a quick benchmark for sailboats, fishing boats and small yachts; exceeding it requires a semi-planing or planing hull form.

Science

Enter your swatch gauge (stitches per 10 cm and rows per 10 cm) and the finished width and height you want; the tool gives the cast-on stitch count and total rows — avoiding the classic "finished sweater is the wrong size" problem.

Lifestyle

Enter the thread's major diameter (mm or in) and pitch or TPI; the tool applies tap_drill = D − (%/100) × 1.0825 × pitch to give the required drill — the everyday tap-drill chart for tapping, machining and DIY woodworking, with 50–100 % engagement adjustment.

Science

Enter the bolt diameter (mm or in), target clamp load (preload, kN or lbf) and nut friction factor K (dry 0.20, oiled 0.15, anti-seize 0.10); the tool applies T = K·F·d to give the recommended tightening torque — essential for mechanical assembly and maintenance.

Science

Enter aircraft (or UAV) mass and wing area; the tool returns W/S (N/m² or lb/ft²) — a fundamental performance parameter: high W/S = stable cruise but long takeoff and high stall speed; low W/S = short takeoff and agile, but gust-sensitive.

Science

Enter the gross trailer weight (GTW), target tongue-weight ratio (10–15 % for conventional, 20–25 % for fifth-wheel) and the measured tongue weight; the tool checks whether you are inside the safe band and suggests how to redistribute the load — preventing highway sway and fishtailing.

Lifestyle

Enter pass attempts (ATT), completions (CMP), passing yards (YDS), touchdowns (TD) and interceptions (INT); the tool applies the four-component formula the NFL has used since 1973 to give the 0–158.3 passer rating, the tier (perfect 158.3 down to poor) and the four sub-scores.

Math

Enter two apparent magnitudes; the tool applies Pogson's law m₁ − m₂ = −2.5 × log₁₀(F₁/F₂) to give the brightness (flux) ratio between any two stars, planets or deep-sky objects, and can convert apparent to absolute magnitude given distance.

Science

Enter planned production time, actual run time, ideal cycle time and total / good unit counts; the tool computes OEE = Availability × Performance × Quality — the universal manufacturing KPI (world-class ≥ 85 %) used in lean management and TPM — and breaks out each of the three component factors.

Math

Enter resistance (Ω) and either voltage (V) or current (A); the tool applies P = V²/R = I²R to give power dissipation (W) and recommends the next-up standard 1/8 W, 1/4 W, 1/2 W, 1 W or 2 W package (with a 50 % safety margin).