A guide to SI units and their usage

A GUIDE TO SI UNITS AND THEIR USAGE Physical quantities like weights and measures have been standardized through a network of international agreements which collectively form the SI or International System of Units (with the French name Système International d'Unités). Written by William Stevenson, an English editor with Enago.com based out of the USA. The system is maintained by the International Bureau of Weights and Measures in Paris, and is updated every few years. SI base units and symbols Quantity Length Unit Symbol meter m Mass kilogram kg Time second Electric Current A ampere kelvin Temperature Amount of substance K mole mol Luminous intensity candela cd SI consists of base units which are absolute and independent of each other. The base units are consistent with the metric system (referred to as the MKS system), with the acronym indicating the first letters of the symbols associated with the units of measurement of length, mass and time. The physical quantities, associated SI units and symbols are illustrated in the adjoining table. In addition to the base units, there are two types of units derived from the base ones, those with and without special names associated with them. Specific prefixes are associated with different factors corresponding to the factor of the SI unit, like kilo for thousand, mega for million and giga corresponding to billion. The kilogram is the only SI unit which has the prefix built into the unit. © enago