Online calculators, fast and complete

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

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

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

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