Length, weight, volume, temperature, speed, area, data and time, both ways as you type
Runs in your browser. Nothing you type is sent anywhere. Checked against sources on 6 Oct 2026.Pick a kind of measurement, choose two units and type in either box; the other box and every related unit update as you type. Factors are exact NIST definitions, so 1 mile is 1.609344 km, 1 pound is 0.45359237 kg and 1 US gallon is 3.785411784 liters.
Pick what you are measuring: Length, Weight, Volume, Temperature, Speed, Area, Data size or Time.
Choose the unit for each of the two boxes, or press Swap to turn them round.
Type a number in either box; the other box changes as you type.
Read the same amount in every other unit under Every unit, and the exact factor under the boxes.
Open Definitions to see where each factor comes from, then press Share result to keep the conversion.
The Unit Converter changes a number between metric, US and UK units of length, weight, volume, temperature, speed, area, data size and time. Type in either of the two boxes and the other one follows, so there is no button to press and no direction to choose. Under the boxes, the same amount is shown in every other unit of that kind.
Where the numbers come from. Every factor is a legal definition, not a rounded table value. NIST Special Publication 811 (the US Guide for the Use of the SI) defines the inch as exactly 2.54 cm, the foot as 0.3048 m, the mile as 1,609.344 m and the pound as exactly 0.45359237 kg. NIST Handbook 44 defines the US gallon as 231 cubic inches and the cup as 8 fluid ounces. The UK gallon is exactly 4.54609 liters. Temperature uses the SP 811 formulas: °F = °C × 1.8 + 32 and K = °C + 273.15. The Definitions tab lists each unit with its definition.
Two kinds of megabyte. A megabyte (MB) is 1,000,000 bytes and a mebibyte (MiB) is 1,048,576 bytes, following the IEC prefixes on NIST's binary-prefix page. Drive makers use GB; Windows reports GiB but labels it GB, which is why a 1 TB drive shows about 931 "GB". Network speeds are in bits: 100 Mbit/s moves 12.5 MB a second.
The acre and the survey foot. Since 1 January 2023 the US uses the international foot for everything, so an acre here is 43,560 square feet, or 4,046.8564 m². SP 811 still prints the old survey-foot acre, which is 0.0004% larger.
Precision. Results show up to 10 significant figures without rounding noise, so 1 foot in inches reads 12, not 11.999999. A share link keeps the kind, both units and the number.
What this converter does not do: cups to grams for an ingredient (that needs a density; use Cups to Grams), Indian land units such as bigha and guntha (Land Area Converter), feet-and-inches arithmetic, shoe sizes or currency.
One mile is exactly 1.609344 kilometers, because the international mile is defined as 5,280 feet of 0.3048 meters each, or 1,609.344 meters. To go from kilometers to miles, multiply by 0.621371. A 10-kilometer race is therefore 6.21 miles, and a 26.2-mile marathon is 42.195 kilometers.
A kilogram is 2.20462262 pounds. The avoirdupois pound has been defined since 1959 as exactly 0.45359237 kilograms, and dividing 1 by that number gives the pounds in a kilogram. For a quick estimate, double the kilograms and add 10 percent: 50 kg is about 110 pounds, exactly 110.23.
Multiply the Celsius temperature by 1.8 (or 9/5) and add 32. So 25 °C is 25 x 1.8 + 32 = 77 °F. For Fahrenheit to Celsius, subtract 32 and divide by 1.8: 98.6 °F is 37 °C. Both scales read the same at minus 40 degrees.
Drive makers count a terabyte as 10^12 bytes, while Windows divides by 2^30 and calls the result GB, though it is really a gibibyte (GiB). One trillion bytes divided by 1,073,741,824 is 931.3 GiB. No space is missing; the two numbers use different prefixes, SI and binary.
No. A US gallon is 231 cubic inches, exactly 3.785411784 liters, and holds 128 US fluid ounces. A UK (imperial) gallon is exactly 4.54609 liters and holds 160 UK fluid ounces, so it is about 20 percent larger. US and UK pints and fluid ounces differ in the same way.
Every factor is the exact legal definition published by NIST, the US National Institute of Standards and Technology: Special Publication 811 for the inch, foot, mile, pound and temperature formulas, Handbook 44 for gallons, cups and tablespoons, and NIST's binary-prefix page for KiB and MiB. The Definitions tab lists each unit.
Rates and rules change; check the source before you rely on a figure.
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