Unit converter
Convert between metric and imperial units for length, weight, temperature, area, volume, speed, data and time. Runs in your browser.
Runs in your browser
Eight categories, one converter
Pick a category, choose your units, and type into either box. Conversion runs in both directions as you type.
Where a conversion is common enough to be worth its own page, it has one: see the related links below for direct pages with the exact factors and reference tables.
Exact versus approximate factors
Some conversions are defined and therefore exact; others are measured and rounded. It is worth knowing which is which:
| Conversion | Exact? | Factor |
|---|---|---|
| inch → centimetre | Exact by definition since 1959 | 2.54 |
| pound → kilogram | Exact by definition | 0.453 592 37 |
| mile → kilometre | Exact (derived from the inch) | 1.609 344 |
| US gallon → litre | Exact by definition | 3.785 411 784 |
| nautical mile → metre | Exact by definition | 1852 |
This converter uses the defined values, so results are limited only by floating-point precision rather than by a rounded constant.
Where the traps are
US and imperial gallons differ. A US gallon is 3.785 L, an imperial gallon 4.546 L, about 20% larger. Pints, quarts and fluid ounces differ correspondingly, which is why recipes crossing the Atlantic go wrong.
Temperature is not a scale factor. Celsius and Fahrenheit have different zero points, so converting requires an offset as well as a ratio. Doubling a temperature in Celsius does not double it in Fahrenheit.
A “year” needs defining. This converter uses the Julian year of 365.25 days, the conventional constant in astronomy. It is not any specific calendar year, and calendar arithmetic across real dates should use a date library rather than a fixed factor.
Data units are ambiguous. A “megabyte” means 1,000,000 bytes to a drive manufacturer and 1,048,576 to some operating systems. Both are offered here separately: MB for the decimal sense, MiB for the binary one.