Unit conversion is the transformation of the numerical value of a physical quantity, expressed in a certain unit of measure, into another equivalent numerical value and expressed in another unit of measure of the same nature.

This process is usually done with the use of conversion factors or unit conversion tables.

Frequently it is enough to multiply by a fraction (factor of a conversion) and the result is another equivalent measure, in which the units have changed. When the change of units implies the transformation of several units, several conversion factors can be used one after another, so that the final result will be the equivalent measure in the units we are looking for.