About CalcPairs

CalcPairs is a small, independent collection of unit converters, built and maintained by the CalcPairs team. It exists for a simple reason: a conversion is a pair — two units and one exact relationship — and it deserves a page of its own, with both directions, the full table, and the constant it stands on printed in the open.

Every factor on this site traces back to an international definition: the inch is exactly 2.54 centimetres, the pound is exactly 0.45359237 kilograms, the US gallon is exactly 3.785411784 litres. Where a unit has more than one living definition — US and UK gallons, the several kinds of ounce and ton — the page says so and lets you choose, instead of quietly picking one for you.

The site is supported by advertising, which is also why it stays free and needs no accounts. Converters run entirely in your browser; the numbers you type are never sent anywhere.

Corrections are welcome. If a constant, a density, or an explanation looks wrong, tell us at [email protected] and we will check it against the source and fix it in the open.