International System of Quantities

The International System of Quantities is a system based on seven base quantities: length, mass, time, electric current, thermodynamic temperature, amount of substance and luminous intensity. Other quantities such as area, pressure and electrical resistance are derived from these base quantities by clear non-contradictory equations. The International System of Units (SI) is based on the International System of Quantities (ISQ) in that the ISQ defines the quantities which are measured with the SI units.^[1] The ISQ is defined in the international standard ISO/IEC 80000.^[2]

References

Further reading

• B. N. Taylor, Ambler Thompson, International System of Units (SI), National Institute of Standards and Technology 2008 edition, ISBN 1437915582.

SI base quantities Base quantity Quantity SI unit Name Symbol Dimension symbol Unit name (symbol) Example length l, x, r, (etc.) L metre (m) r = 10 m mass m M kilogram (kg) m = 10 kg time, duration t T second (s) t = 10 s electric current  I , i  I  ampere (A) I = 10 A thermodynamic temperature T Θ kelvin (K) T = 10 K amount of substance n N mole (mol) n = 10 mol luminous intensity Iv J candela (cd) Iv = 10 cd Specification The quantity (not the unit) can have a specification: Tmax = 300 K Derived quantity Definition A quantity Q is expressed in the base quantities: Derived dimension dim Q = La · Mb · Tc · Id · Θe · Nf · Jg (Superscripts a–g are algebraic exponents, usually a positive, negative or zero integer.) Example Quantity acceleration = l1 · t−2, dim acceleration = L1 · T−2 possible units: m1 · s−2, km1 · Ms−2, etc. See also History of the metric system International System of Quantities Proposed redefinitions Systems of measurement Book Category Outline