**Conversion factors** are used to convert one unit to another (either within the same system or between different systems). A conversion factor is simply a fraction built from two equivalent values. For example, there are 12 inches in 1 foot, so the conversion factor is \(\frac{12\ in}{1\ ft}\) or \(\frac{1\ ft}{12\ in}\).

To convert from one unit to another, multiply the original value by a conversion factor. Choose a conversion factor that will eliminate the unwanted unit with the desired unit.