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Appendix:SI units

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SI units

SI is an abbreviation of Système International (d'Unités) [International System (of Units)] and is a standard metric system of units adopted for official scientific use. For more information, see Wikipedia's article on SI.

Note: this page is simply a collection of links to the names of SI units and their prefixes and multiples. For further information, see the Wikipedia articles SI base units and SI derived units.

Base units (with symbols in parentheses)

Derived units (with symbols in parentheses)

Alternative names for SI units and their multiples and submultiples

Former names for SI units

SI prefixes

prefix sym multiplier notes
yotta- Y 1024
zetta- Z 1021
exa- X 1018
peta- P 1015
tera- T 1012
giga- G 109
mega-, meg- M 106 1
kilo- k 103
hecto- h 102 2
deca-, deka- da 101 2
deci- d 10–1
centi- c 10–2
milli- m 10–3
micro- µ, u 10–6
nano- n 10–9
pico- p 10–12
femto- f 10–15
atto- a 10–18
zepto- z 10–21
yocto- y 10–24


1. meg- is used before a vowel, as in megohm
2. not commonly used

Binary prefixes

The following prefixes are not part of SI. They were adopted by the IEC to express binary multiples.

prefix sym multiplier
exbi- Ei 260
pebi- Pi 250
tebi- Ti 240
gibi- Gi 230
mebi- Mi 220
kibi- Ki 210

Former prefixes

These prefixes were never part of SI.

prefix multiplier equivalent
hectokilo- 105
myria- 104
millimilli- 10–6 micro-
millimicro- 10–9 nano-
micromicro- 10–12 pico-

Commonly used multiples of units

The table below shows which prefixes are most commonly used with each unit. In theory, any combination of a prefix and a unit is possible. In practice, only those multiples that are of practical use are used. Multiples towards the left and right of the table tend to gain currency as advances in technology and miniaturisation make them meaningful.
Links are to combinations that are in relatively common scientific use. Blank entries indicate combinations that are rare or not used.
  1. Units are ordered alphabetically by their symbol. Prefixes are ordered from largest to smallest.
  2. It is the gram (g) that takes prefixes, not the kilogram.
  3. Some combinations have special names; for example, 106 grams is called a tonne, not a "megagram".
  4. The multiples in the grey columns are not in official scientific usage.
  5. The table lists multiples of SI units only. Other units that use the SI prefixes, such as kilobyte and millibar, are not given here.
  6. The table is currently incomplete. More links will be added later.

(Sources: ; Oxford English Dictionary, 2nd ed.)

Commonly used multiples of SI units
Y Z E P T G M k h da Unit d c m μ n p f a z y
MA kA A mA μA nA
PBq TBq GBq Bq
F mF μF nF pF
t, Mg kg hg dag g dg cg mg μg
H mH μH nH
PHz THz GHz MHz kHz Hz
kJ J
klx lx
km hm dam m dm cm mm μm nm pm fm
mol mmol μmol
GPa MPa kPa hPa Pa
rad mrad
s ms μs ns ps fs as
Sv mSv µSv
T mT µT nT
MV kV V mV μV
GW MW kW W mW μW
kWb Wb mWb μWb