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Converters translate between units across length, area, volume, weight, temperature, speed, time, data and more. Each converter uses exact international definitions where they exist: the metre, the kilogram, the 1959 international yard and pound agreement, and the SI brochure. Enter one value and read every equivalent instantly, with precision that stays traceable to the standard rather than rounded intermediates. Conversion tables for common everyday values are included, along with tips for mental conversions. It also carries the specialised engineering converters: flow rate, torque, radiation dose, magnetic field and data rate, where a field has its own conventions such as gauge systems or historical units. All converters run entirely in your browser. If you are working to a standard, check the unit conventions that standard expects, because a few fields still use historical local measures alongside the SI values. The converters share one interface, so once you have used one, the rest feel familiar, and every page links to the related conversion tools in the same family.
Method and definitions follow NIST Special Publication 811, Guide for the Use of the SI.
The conversions assume the exact international definitions named on each page; they do not adjust for the historical or local measures that a few fields still use.
Worked example. Inputs: 12 inches. Result: 30.48 centimetres, because the international inch is exactly 25.4 millimetres and 12 x 25.4 = 304.8 mm.
Limits and assumptions. Every converter assumes the standard definition of each unit, so a trade that still prices in local or historical measures will not match, and a figure rounded for display is not a substitute for the tolerance on a drawing.
Sources and standards: NIST Special Publication 811, Guide for the Use of the International System of Units (SI)
Worked scenarios
Illustrative examples. Every figure was calculated with the tools linked at the foot of each scenario, using the formula each tool documents, so the numbers can be reproduced. They are not client results and they are not advice.
A 10 km race is 6.2137 miles, using the exact international definitions of the kilometre and the mile. A half marathon of 21.0975 km is 13.1094 miles. Reading the pace in kilometres and the distance in miles is where most errors come from, so the converter shows both units at once.
Worked with: Kilometers to Miles Converter, Unit Converter
An oven set to 180 degrees Celsius is 356 degrees Fahrenheit by the standard conversion, which multiplies by 9/5 and adds 32. A 200 C recipe is 392 F. Because the two scales have different step sizes, a five degree change on one scale is a nine degree change on the other.
Worked with: Celsius to Fahrenheit Converter, Temperature Converter
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Convert square measurements between metric, imperial, acres, and hectares.
Convert knots, miles per hour, kilometres per hour, metres per second, and feet per second, nautical, road, and aviation speeds.
Convert a 6-digit or 3-digit hex colour to HSL (Hue, Saturation, Lightness) using the W3C CSS Color Module Level 4 algorithm, with live swatch, WCAG contrast, and palette generation.
Convert hex colour codes to RGB, HSL, CMYK, and a live preview swatch.
Convert ASCII text to hexadecimal bytes and back, bidirectional encoder/decoder.
Decode a stream of ASCII codes (decimal, hex, octal, or binary) back into readable text with separator and prefix options.
Length, weight, volume, temperature, and more.
Celsius, Fahrenheit, and Kelvin.
Convert between km, miles, feet, inches, and more.
Convert between kg, lbs, stone, and more.
Convert between mph, km/h, m/s, and knots.
Convert between Roman numerals and numbers.
Convert shoe sizes between US, UK, and EU.
Convert any color between HEX, RGB, HSL, and HSV/HSB. Live swatch, per-format validation, and quick presets for common web colors.
Bidirectional cm ⇄ mm ⇄ inches with metres and feet read-outs.
Tyre diameter, circumference, and speedometer error from size codes.
International clothing and shoe sizes across US, UK, EU, JP, and AU.
Convert ring sizes between US, UK, EU systems with diameter chart.
Convert between digital storage units instantly.
Convert between energy units, joules, kilojoules, kilowatt-hours, BTUs, calories, kilo...
Convert between power units, watts, kilowatts, megawatts, horsepower, BTU/hour, and more.
Convert Celsius to Fahrenheit and Fahrenheit to Celsius instantly. Bidirectional sync with quick-preset reference points.
Convert Fahrenheit to Celsius and Celsius to Fahrenheit instantly using the exact 9/5 and 32 definitions. Includes Kelvin bonus read-out.
Convert Fahrenheit to Kelvin (and Kelvin to Fahrenheit) instantly. Shows Celsius as a bonus and Rankine. 0 K = −459.67 °F = −273.15 °C exactly.
Convert avoirdupois ounces (oz) to grams (g) and back, also kilograms, milligrams, pounds, and troy ounces.
Convert US cups to grams (and back) for eight common baking ingredients, water, flour, sugar, butter, honey, olive oil, milk, and rice, with bidirectional sync.
Convert stones to kilograms and kilograms to stones instantly with the full UK body-weight breakdown (1 st = 14 lb = 6.35029318 kg = 224 oz).
Convert BTU per hour to watts and watts to BTU/h instantly. Bidirectional sync with HVAC presets for window AC, central AC, heat pumps, and space heaters.
Convert lumens to watts and watts to lumens instantly with luminous-efficacy presets for incandescent, halogen, CFL, LED, and high-efficiency LED light sources.
Convert numbers between binary, octal, decimal, and hexadecimal instantly. Pick a source base, type a value, and read the same number in all four bases.
Convert between metric and imperial mass units: kilograms, grams, pounds, ounces, stones and tonnes.
Convert between volume units: litres, millilitres, cubic metres, US/UK gallons and cubic feet.
Convert shoe and clothing sizes between US, UK, EU, JP, AU, and more.
Convert between feet, metres, inches, yards, miles and all length units.
Convert between millimetres, centimetres, metres, and inches with sub-mm precision.
Generate Code 128, Code 39, EAN-13, and UPC-A barcodes client-side. Download as SVG or PNG.
Calculate width and height while maintaining an aspect ratio. Presets for 16:9, 4:3, 21:9, 1:1, 4:5, 9:16, plus custom ratios.
Convert between bits, bytes, KB, MB, GB, TB, KiB, MiB, GiB, TiB, decimal (SI) and binary (IEC) modes.
Convert between L/100km, MPG (US), MPG (UK), and km/L instantly.
Convert AWG wire gauge and sheet-metal gauge to millimetres and inches. Material-specific sheet tables (steel, aluminium), AWG reverse lookup, mm² area.
Convert torque between newton-metres (N·m), kilogram-force metres (kgf·m), pound-force feet (lbf·ft), pound-force inches (lbf·in), and ounce-force inches (ozf·in). Five synced fields with fastener presets.
Convert CSV to JSON in your browser. RFC 4180 parser handles quoted commas, newlines and escaped quotes. Pick delimiter, header, trim and type coercion.
Convert any data transfer rate between bit/s, kbit/s, Mbit/s, Gbit/s, Tbit/s, byte/s, kB/s, MB/s, GB/s and the IEC binary set KiB/s, MiB/s, GiB/s, all pivoted through bit/s so twelve fields stay in sync. Includes a download-time panel.
Convert volumetric flow rate between m³/s, m³/h, L/s, L/min, L/h, US GPM, US GPH, Imperial GPM, ft³/s (CFS) and ft³/min (CFM). Ten synced fields plus a pipe-velocity panel.
Convert dynamic viscosity (Pa·s, mPa·s, poise, cP, lbf·s/ft², lb/(ft·s)) and kinematic viscosity (m²/s, stokes, cSt, mm²/s, ft²/s) with a density bridge between the two panels.
Convert magnetic flux density (T, mT, µT, G, mG, γ), magnetic flux (Wb, Mx), and magnetic field strength (A/m, Oe). Includes a free-space B↔H bridge and a reference table of real-world field magnitudes.
Convert absorbed dose (gray, rad), equivalent dose (sievert, rem, mSv, µSv, mrem), activity (becquerel, curie) and exposure (C/kg, roentgen) across four independent panels.
Convert plain text to and from Grade-1 Braille Unicode instantly in your browser, letters, numbers, and punctuation with copy-paste support.
Convert kilograms to pounds (and pounds to kilograms) using the exact international avoirdupois factor. Free online kg ↔ lb calculator.
Convert watts to mechanical and metric horsepower (and back).
Convert centimetres to inches and inches to centimetres instantly using the exact 2.54 cm/in factor.
Convert knots to kilometres per hour and back using the exact 1.852 factor. Includes bonus m/s and mph read-outs.
Convert kilometres to statute miles (and miles to kilometres) instantly using the exact 1.609344 km/mi factor. Includes pace and metres/feet/yards read-outs.
Convert metres to yards and yards to metres instantly using the exact 0.9144 m/yd factor. Shows centimetres, millimetres, feet and miles too.
Convert metres to feet and feet to metres instantly using the exact 0.3048 m/ft factor. Shows inches and centimetres too.
Convert RGB colour values (0 to 255 per channel) to a hex code and back, with a live preview swatch.
Convert pints to litres (and litres to pints) for both UK imperial and US liquid pints. Live cross-update with fl oz and mL read-outs.
Convert kilograms to UK stones (and back) using the exact factor 1 stone = 14 pounds = 6.35029318 kg. Shows canonical "X st Y lb" form for body weight plus bonus read-outs in kg, g, lb, oz and US short tons.
Convert any text to its ASCII code points in decimal, hex, or binary, and decode a numeric code stream back into text. Includes a per-character breakdown.
Convert between miles and yards with full precision. 1 mile = 1 760 yards exactly.
Convert between atmospheres (atm) and pascals (Pa). 1 atm = 101 325 Pa exactly.
Convert between bar and pounds per square inch (psi). 1 bar = 14.5037738 psi exactly.
Convert between millimetres (mm) and feet (ft) with full precision. 1 ft = 0.3048 m exactly.
Convert between torr/mmHg and pascals (Pa). Vacuum science, chemistry, medicine.
Convert decimal integers and fractions to binary, octal, and hexadecimal. Bidirectional dec ⇄ bin with bonus oct and hex read-outs.
Convert between US gallons, UK (imperial) gallons, and liters. 1 US gal = 3.785411784 L exactly; 1 UK gal = 4.54609 L exactly.
Bidirectional litre ↔ US/UK gallon converter with strict NIST factors and cross-displayed millilitres.
Convert cups to milliliters (US legal, US customary, metric). 1 US legal cup = 240 mL exactly. 1 metric cup = 250 mL exactly.
Convert centimeters to feet and inches (and back). 1 inch = 2.54 cm exactly; 1 foot = 30.48 cm exactly. Includes m, mm, yd, decimal ft/in.
Convert horsepower (mechanical hp(I), metric PS/CV, boiler hp(S), electrical hp(E)) to kilowatts. 1 hp(I) = 0.7456998715822702 kW exactly.
Convert Kelvin to Fahrenheit and Fahrenheit to Kelvin instantly. Shows Celsius and Rankine bonus. 0 K = −459.67 °F = −273.15 °C exactly.
Convert joules to calories (thermochemical), kilocalories, and kilowatt-hours. 1 cal = 4.184 J exactly.
Convert inches to feet and feet to inches instantly. 1 foot = 12 inches exactly (US customary, NIST SP 811). Includes yards, cm, m, mm read-outs and a combined feet+inches form.
Convert Kelvin to Celsius and Celsius to Kelvin instantly. The 273.15 offset is exact by SI definition (BIPM SI Brochure §2.3.1, NIST SP 811). Includes Fahrenheit and Rankine bonuses, round-trip drift indicator, and physical-reference presets (absolute zero, liquid nitrogen, dry ice, lab temp).
Convert square feet to acres and acres to square feet instantly. 1 acre = 43,560 ft² exactly (US survey definition; NIST SP 811). Includes m², hectares, yd² bonus read-outs.
Convert binary to octal instantly using the 3-bit grouping shortcut, and see decimal and hexadecimal at the same time. Shows the padded bit groups step by step, validates every digit, and uses BigInt so long bit strings stay exact.
Convert US cups to tablespoons (and back) instantly. 1 US cup = 16 US tablespoons exactly. Bonus readouts for teaspoons, fluid ounces, and millilitres.
Convert yards to feet and feet to yards instantly. 1 yard = 3 feet exactly (NIST SP 811). Includes metres, centimetres, millimetres, kilometres, inches, and miles bonus read-outs with a results table.
Convert hexadecimal to binary using the exact 4-bit grouping shortcut, with octal and decimal shown alongside. Shows the padded nibble groups step by step, validates every digit, and uses BigInt so long hex strings stay exact.
Convert pounds to stones and stones + pounds to kilograms using the exact UK definition (1 st = 14 lb, 1 lb = 0.45359237 kg by the 1959 international yard-and-pound agreement). Shows kg, g, oz, US short tons alongside.
Convert statute miles to kilometres and vice versa using the exact factor 1 mi = 1.609344 km (international yard-and-pound agreement of 1959). Bonus read-outs in metres, feet and yards.
Convert inches to centimetres and vice versa using the exact factor 1 in = 2.54 cm (international yard-and-pound agreement of 1959). Bonus read-outs in mm, m, feet and yards.
Convert joules to BTU (International Table) and BTU to joules. 1 BTU(IT) = 1 055.05585262 J exactly (NIST SP 811). Bonus read-outs in kJ, kWh, cal, kcal, ft·lbf.
Convert hexadecimal numbers (0x...) to decimal, binary, and octal instantly with strict input validation.
Convert decimal (base-10) integers to hexadecimal, binary, and octal instantly with strict input validation.
Convert octal numbers (0o...) to decimal, binary, and hex instantly with strict input validation, perfect for Unix file permissions.
Convert between pascals, bar, atmospheres, psi, torr, mmHg, inHg and more with live results.
Convert angles between degrees, radians, gradians, turns, arcminutes, arcseconds, milliradians and NATO mils, with DMS notation and live results.
Convert illuminance between lux, foot-candles, phot, nox, lumen/m² and lumen/ft², with reference lighting levels and a live results table.
Convert density between kg/m³, g/cm³, lb/ft³, lb/gal, slug/ft³, tonne/m³ and more. Live results table, material presets, specific-gravity readout.
Reference and converter for ISO A/B/C and North American paper sizes, mm, cm, inches, points, and pixels at 72/150/300/600 DPI.
Convert fuel economy between MPG (US/UK), km/L, L/100km, L/10km, L/km, miles/L, and km per US/UK gallon, with a cost-per-distance helper.
Convert wire gauge between AWG, SWG, BWG, mm² cross-sectional area, mm and inch diameter. Includes copper resistance per km at 20 °C (IEC 60228) and an ampacity reference panel (NEC NFPA 70 Chapter 9 Table 8 family).
Convert milligrams (mg) to grams (g) and back, with quick presets for medicine doses, kitchen measures, and chemistry lab quantities.
Convert days (d) to hours (h) and back, with quick presets for shifts, weeks, months, and years.
Convert watts (W) to kilowatts (kW) and back, with quick presets for appliances, lighting, heaters, and small industrial loads.