Unit converter

How these converters differ

Each pair has its own page with the exact conversion factor, the formula written out, and a full reference table — not only an input box. Where a relationship is exact by definition we say so, and where it is a rounded approximation we say that too.

Everything runs in your browser. Nothing you type is sent to a server, and once the page has loaded the converter keeps working offline.

Most of these relationships are exact by definition rather than measured. An inch has been exactly 25.4 mm and a pound exactly 0.45359237 kg since the 1959 international yard and pound agreement, which is why these pages print a factor without a source date beside it — it cannot go out of date. Temperature behaves differently: Celsius and Fahrenheit are related by an offset as well as a ratio, so there is no single “one degree equals N degrees” figure and those pages print the formula instead.

Volume here is US measure, and that matters more than it looks. A US gallon is 3.785411784 L and a US fluid ounce is 29.5735 mL. The imperial gallon still used in the UK is 20.1% larger and the imperial fluid ounce is 3.9% smaller. A 16 fl oz bottle is not the same bottle on both sides of the Atlantic, so a label converted without checking which ounce was meant is a labelling error rather than a rounding one.

Round in the direction that costs least to be wrong about. These pages show six significant figures because a spec sheet needs them, but a shipping label does not: carriers bill on a chargeable weight rounded up to the next increment, so a parcel that converts to 2.02 kg is charged as a heavier one. If that is the number you are actually chasing, convert it inside the landed cost rather than on its own.

Export pricing calculator — works out chargeable weight, duty, tax and freight together