Measurement System Basics

International System of Units

For weights and measures such as length, the same measurement should, in principle, have the same unit anywhere in the world. To that purpose, the International System of Units was defined during the General Conference on Weights and Measures (CGPM) in 1960. The abbreviation "SI" comes from the name of this system in French, Le Système International d'Unités.
In the International System of Units, the metre (m) is used as the SI unit (base unit) of length. SI prefixes are written in front of the unit. For example, "km" includes the prefix k (kilo; 10 to the power of 3) followed by m.

SI base unit
Material Name Symbol
Length Metre m
SI prefixes (symbols that indicate integral multiplications of 10)
Symbol Symbol Exponential representation Value to multiply the unit by
Mega M 1 × 106 1,000,000
Kilo k 1 × 103 1,000
- - 1 × 100 1
Centi c 1 × 10-2 0.01
Milli m 1 × 10-3 0.001