# International System of Quantities

The **International System of Quantities** (**ISQ**) consists of the quantities used in physics and in modern science in general, starting with basic quantities such as length and mass, and the relationships between those quantities.[lower-alpha 1] This system underlies the International System of Units (SI)[lower-alpha 2] but does not itself determine the units of measurement used for the quantities. It is inherently incomplete because the number of quantities is potentially infinite.

The system is formally described in a multi-part ISO standard ISO/IEC 80000, first completed in 2009 but subsequently revised and expanded.