National Physical Laboratory

SI Prefixes

SI prefixes are used to form decimal multiples and submultiples of SI units.

They should be used to avoid very large or very small numeric values.

The prefix attaches directly to the name of a unit, and a prefix symbol attaches directly to the symbol for a unit.

 

Multiplying Factor SI Prefix Scientific Notation
1 000 000 000 000 000 000 000 000 yotta (Y) 1024
1 000 000 000 000 000 000 000 zetta (Z) 1021
1 000 000 000 000 000 000 exa (E) 1018
1 000 000 000 000 000 peta (P) 1015
1 000 000 000 000 tera (T) 1012
1 000 000 000 giga (G) 109
1 000 000 mega (M) 106
1 000 kilo (k) 103
0.001 milli (m) 10-3
0.000 001 micro (µ) 10-6
0.000 000 001 nano (n) 10-9
0.000 000 000 001 pico (p) 10-12
0.000 000 000 000 001 femto (f) 10-15
0.000 000 000 000 000 001 atto (a) 10-18
0.000 000 000 000 000 000 001 zepto (z) 10-21
0.000 000 000 000 000 000 000 001 yocto (y) 10-24