unitbox – Free Unit Converter

unitbox is a free unit converter that runs in the browser. It covers 12 categories – length, mass, temperature, area, volume, speed, time, data storage, energy, pressure, angle and fuel economy – across 24 conversion pairs plus a general calculator. No account, no install, nothing sent to a server.

What separates it from a plain converter is that each page explains the number it just gave you: the rate in both directions (1 m = 3.2808 ft), a ten-value reference table around your input, the definition each unit is based on, and which convention the result assumes. That last part is where converters usually mislead. A US gallon is exactly 3.785411784 litres, an imperial gallon is 4.54609. A kilobyte is 1000 bytes decimal, a kibibyte 1024 binary. unitbox labels the one it used instead of quietly picking one and leaving you to guess.

Pages also carry a short FAQ, related conversions and a link to the methodology, so it holds up as a reference while studying or on site, not just for a single lookup.