How conversions work
Every unit is stored with an exact conversion factor to a base unit (meters, kilograms, liters, square meters or meters per second). To convert, the value is multiplied by the "from" factor and divided by the "to" factor. The factors use the official international definitions, for example 1 inch = 2.54 cm and 1 pound = 0.45359237 kg exactly.
Temperature isn't a simple ratio because the scales have different zero points, so it's converted through Celsius:
Common conversions
| 1 inch | 2.54 cm |
| 1 foot | 30.48 cm |
| 1 mile | 1.609344 km |
| 1 pound | 0.4536 kg |
| 1 kilogram | 2.2046 lb |
| 1 US cup | 236.59 mL |
| 1 US gallon | 3.7854 L |
| 1 acre | 43,560 ft² |
| 100 km/h | 62.14 mph |
US and UK (imperial) volume units differ: a UK gallon is about 20% larger than a US gallon, and UK fluid ounces are slightly smaller. Cooking units here are US customary.
Next steps
Converting for a project? The square footage and concrete calculators accept feet and inches directly.
Frequently asked questions
How many cups are in a liter?
About 4.23 US cups. A US cup is 236.59 mL. Note that US nutrition labels round a cup to 240 mL.
Is a stone a unit of weight?
Yes. A stone is 14 pounds (6.35 kg), commonly used for body weight in the UK and Ireland.
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