Metric, imperial and US units
Most of the world uses the metric system: meters, grams, liters. The United States still uses US customary units, and the United Kingdom uses a mix of metric and imperial units. Since 1959 the inch, foot, yard, mile and pound are defined through metric units, so conversions between them are exact: one inch is 2.54 cm and one pound is 0.45359237 kg.
Same name, different size
Watch out for units that share a name but not a size:
- Gallons and pints. A US gallon is 3.785 L, an imperial (UK) gallon is 4.546 L. A US pint is 473 mL, a UK pint is 568 mL.
- Tons. A metric tonne is 1000 kg, a US short ton is 907 kg.
- Horsepower. Metric horsepower (PS) is 735.5 W, mechanical horsepower (hp) is 745.7 W.
- Kilobytes. A kilobyte (kB) is 1000 bytes, a kibibyte (KiB) is 1024 bytes.
How the converter works
Every unit is stored with its exact factor relative to a base unit (the meter, the kilogram, the liter and so on). The value is converted to the base unit and then to the target unit. Temperature and fuel consumption need formulas rather than a single factor, and the converter uses them. Results are rounded to ten significant digits.