# SI Prefixes Table

Example: 1 TW=1000 GW (W=Watt)

Symbol | Prefix | Factor
--- | --- | ---
Y | Yotta | 1024
Z | Zetta | 1021
E | Exa | 1018
P | peta | 1015
T | tera | 1012
G | giga | 109
M | Mega | 106
k | kilo | 103
h | hecto | 102
da | deca | 101
d | deci | 10-1
c | centi | 10-2
m | milli | 10-3
µ u | micro | 10-6
n | nano | 10-9
p | pico | 10-12
f | femto | 10-15
a | atto | 10-18
z | zepto | 10-21
y | yokto | 10-24

Note: In the computer world things are a bit different:

Symbol | Prefix | Factor | Factor
--- | --- | --- | ---
P | peta | 250 | 1125899906842624
T | tera | 240 | 1099511627776
G | giga | 230 | 1073741824
M | Mega | 220 | 1048576
k | kilo | 210 | 1024

There is also the prefixes adopted by IEC in order to cope with the digital world. These are not widely used (yet).

Symbol | Prefix | Factor | Factor
--- | --- | --- | ---
Ei | exbi | 260 | 1152921504606846976
Pi | pebi | 250 | 1125899906842624
Ti | tebi | 240 | 1099511627776
Gi | gibi | 230 | 1073741824
Mi | mebi | 220 | 1048576
Ki | kibi | 210 | 1024

Contributor: | Joakim Ögren, Haudy Kazemi, Knut Kristan Weber Daniel Nilsson

Source: | Farnell Components Catalogue

Copyright © The Hardware Book Team 1996-2004.
May be copied and redistributed, partially or in whole, as appropriate.
Document last modified: 2002-01-13