Conversion Calculators

Unit conversion looks trivial until the units are not what you assumed. A US gallon is not an imperial gallon, a US ton is not a metric tonne, and a fluid ounce measures volume while an ounce measures weight — they are only interchangeable for water, and only roughly. These converters state the exact factor they use, so you can see what standard the answer is built on.

For length, weight and volume, the conversion is a single multiplication and the calculators show the factor as well as the result, which makes them useful for checking work rather than only producing it. Temperature is the exception: Celsius and Fahrenheit have different zero points as well as different step sizes, so the conversion is a formula rather than a factor, and Kelvin shares Celsius's step size but starts at absolute zero.

Where precision matters, use the exact definitions rather than the rounded ones. One inch is exactly 25.4 millimetres by international agreement, one pound is exactly 0.45359237 kilograms, and one mile is exactly 1,609.344 metres. Rounding those to 25, 0.45 and 1,600 is fine for a mental estimate and not fine for anything that gets machined, dosed or invoiced.