Diopter ↔ Focal Length Converter

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

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

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

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

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

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 …).

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

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

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.

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.

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

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.

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

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

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.

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.

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.

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.

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

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).

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

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

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

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

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

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.