About Free Unit Converter

Free Unit Converter converts 492 units across 17 categories, from everyday metric and imperial units to ancient and regional measures such as the cubit, tsubo, tola and Roman mile.

Who I am

Hi, I'm Tim. I work in the engineering field, where the right unit and the right conversion factor matter every day. I also have a keen interest in other cultures and in history, and measurement is one of the most revealing places where the two meet: how a people measured land, grain, cloth or distance says a lot about how they lived.

Why I built this site

I built it as a reference for my own work and personal study, a single place to check a conversion and read about where a unit came from. It turned out to be useful enough that I wanted to share it with everyone.

How conversions work

Every unit is defined by an exact ratio to a base unit (for example the meter), stored as an exact fraction rather than a rounded decimal. Results are calculated with exact arithmetic and rounded only for display, to 10 significant digits. Where a definition is exact (for example 1 inch = 25.4 mm) the page says so.

Historical units

Many historical units had no single standard: a foot, pound or gallon could differ between cities and centuries. For those, we use the most commonly cited modern equivalent and mark the unit as approximate.

Found a mistake?

Please email me at hello@free-unit-converter.com with the unit and the value you expected. — Tim