A unit is a measurement of a quantity that is defined or adopted by tradition or law. Other quantities can be expressed as a multiple of the unit.

In human history, various unit systems were developed and used in different regions and cultures. Currently, the global standard of measurement is the International System of Units (SI), which is a modern form of the metric system. Although SI is intended for global use, it has not been fully adopted, and some other systems of measurement are still used in parts of the world.

The intent of this site is to provide a convenient means to convert between the various units of measurement within different systems, as well as to provide a basic understanding of the systems currently in use, and how they interact. Refer to the Common Unit Systems page for further information.