Unit converter
Choose a kind of measure, type a value, and read it in every unit of that kind at once.
- Eight kinds of measure
- Exact definitions
- Every unit at once
In every unit
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Exact by definition
Imperial and US units are no longer measured against physical objects: each is defined as an exact number of metric units. The converter uses those definitions, so its figures are exact up to the last digit shown.
| Unit | Defined as |
|---|---|
| 1 inch | 25.4 mm |
| 1 foot | 0.3048 m |
| 1 mile | 1,609.344 m |
| 1 pound | 0.45359237 kg |
| 1 US gallon | 231 cubic inches, or 3.785411784 L |
| 1 imperial gallon | 4.54609 L |
| 1 acre | 4,840 square yards, or 4,046.8564224 m² |
| 1 knot | 1.852 km/h |
The inch and the pound have been fixed this way since the international agreement of 1959.
US and imperial measures are not the same
The United States and the old British system share names, not sizes. A US pint is 473 mL and an imperial pint 568 mL. A US gallon is 3.785 L and an imperial gallon 4.546 L, which is why fuel economy in miles per gallon differs between the two. A US cup is about 237 mL, while Canadian measuring cups are usually 250 mL: the metric cup. For weights, a US ton is 2,000 pounds, a British ton 2,240, and a tonne 1,000 kilograms.
The converter lists each of these under its own name, so there is no guessing which one a figure means.
Temperature is the exception
Most units differ by a factor. Temperature scales also start at different points, so converting takes a formula rather than a multiplication.
The two scales meet at −40, the one temperature that reads the same in both.
Kilobytes and kibibytes
A kilobyte (kB) is 1,000 bytes; a kibibyte (KiB) is 1,024. Drive makers count in the first, most operating systems in the second while still writing “GB”. That is why a 1 TB drive shows as about 931 GB: it holds 931 gibibytes, which is the same trillion bytes.
Need a percentage rather than a unit? See the percentage calculator.
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