The SI system, which is continually evolving, can be defined as follows:

The International System of Units (abbreviated as SI) is the modern form of the metric system, and is the most widely used system of measurement. It comprises a system of units of measurement built on seven base units and derived units which are formed by powers, products or quotients of the base units and are unlimited in number (for example velocity is a quantity that is derived from the base quantities of time and length).

**Base units**

kg for mass,

sec for time

meter for length

kelvin for temperature

ampere for current

mole for the molecular weight

candela for luminous intensity

The SI system is intended to be an evolving system, so prefixes and units are created and unit definitions are modified through international agreement as the technology of measurement progresses and the precision of measurements improves.