Unit converter
Length, mass, volume, temperature and more.
About this calculator
Choose a measure and two units, and you get the converted value along with the same amount in every other unit.
US and UK volumes differ, so pints and gallons are listed separately for each: a US gallon is about 3.79 litres, and a UK gallon is about 4.55 litres.
How it works
Converts through a base unit using exact definitions, such as 1 inch = 2.54 cm.
Worked example
- Measure: Length
- Value: 1
- From: Mile
- To: Kilometre
1 Mile =: 1.609344 (Kilometre)
The story behind it
Where the idea came from: The metric system, France, 1790s.
The metric system came out of the French Revolution as a single system for everyone. In 1959, several English-speaking countries agreed the exact metric values of the inch and the pound. Mix-ups still matter: NASA lost the Mars Climate Orbiter in 1999 after a mismatch between US customary and metric units. This converter works through exact definitions, so the numbers stay consistent.
Why you can trust this calculator
- It runs in your browser. Nothing you type into it is sent anywhere.
- The method is explained on this page, so you can check it yourself.
- Free to use, with no sign-up.
- Results are estimates, so please double-check anything important.
- Spotted a mistake? Tell us and we'll look into it.
After 15 years as a mathematics educator, I built CalculStore to give students, teachers, professionals and anyone working with numbers simple, reliable tools.
Meet the founder