Unit converters

A conversion is usually a single multiplication, and the 11 categories below cover 630 unit pairs between them. Most of the factors are exact by definition rather than measured: an inch has been exactly 2.54 centimetres since the 1959 international agreement on the yard and pound, so converting inches to centimetres introduces no rounding error at all. The metric system works the same way, because its prefixes are powers of ten.

Two families need more care. Temperature is an affine scale with no shared zero point, so Celsius, Fahrenheit and Kelvin need an offset as well as a multiplier — multiplying Celsius by a factor alone gives the wrong Fahrenheit figure. Data storage has two competing conventions as well: this site converts in binary throughout, where 1 KB is 1,024 bytes, while drive manufacturers use decimal powers of ten where 1 kB is 1,000 bytes. That mismatch is why a disk sold as 500 GB reads as roughly 465 GB in a file manager.

Every unit has its own page listing what it converts to, with the exact figure for each target worked through the same engine as the converter above, plus examples and the rounding behaviour to watch for. Each category also carries an accuracy note explaining where a competing definition can make the last digit disagree.