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International System of Units Appendix G
SI Supplementary Units
SI Derived Units
To indicate decimal multiples or submultiples of these units, the following list of prefixes was established. For
example, the hectopascal (hPa), a unit commonly heard in weather forecasts, is one pascal (Pa) multiplied by
10
2
, which is indicated by adding the prefix hecto (h). The current SI units specify 20 prefixes from 10
24
to
10
-24
. For practical purposes, these units are also used in combination with time units (minute, hour, and sec-
ond), angle units (degree, minute, second), volume units (liter), and mass units (ton).
SI Unit Prefixes
Quantity Unit name Unit
symbol
Definition
Plane angle Radian rad A radian is the plane angle between two radii of a circle that cuts
off on the circumference an arc equal in length to the radius.
Solid angle Steradian sr A steradian is the solid angle that, having its vertex in the center of
a sphere, cuts off an area of the surface of the sphere equal to that
of a square with sides equal in length to the radius of the sphere.
Quantity Unit name Unit
symbol
Expressed in terms of other
SI units
Plane angle radian rad ---
Solid angle steradian sr ---
Frequency hertz Hz
1 Hz = 1 s
−
1
Force newton N
1 N = 1 kg·m·s
−
2
Pressure, stress pascal Pa
1 Pa = 1 N·m
−
2
Energy, work, quan-
tity of heat joule J 1 J = 1 N·m
Power, radiant flux watt W
1 W = 1 J·s
−
1
Electric charge,
quantity of electricity coulomh C 1 C = 1 A·s
Electric potential,
electromotive force volt V
1 V = 1 W·A
−
1
Electric capacitance farad F
1 F = 1 C·V
−
1
Electrical resistance ohm
Ω
1
Ω
= 1 V·A
−
1
Electric conductance siemens S
1 S = 1 A·V
−
1
Magnetic flux weber wb 1 wb = 1 V·s
Magnetic flux density tesla T
1 T = 1 wb·m
−
2
Inductance henry H
1 H = 1 wb·A
−
1
Temperature degree Celsius
°
C t
°
C = (t + 273.15) K
Luminous flux lumen lm 1 lm = 1 cd·sr
Illuminance lux lx
1 lx = 1 cd·s·rm
−
2
Multiple Prefix
Symbol Name
10
−
24 y yocto
10
−
21 z septo
10
−
18 a atto
10
−
15 f femto
10
−
12 p pico