SI base units used on

Type Name Symbol
length metre m
mass kilogram kg
time second s
electric current ampere A
temperature kelvin K
amount of substance mole mol
luminous intensity candela cd

SI derived units used on

Type Name Symbol
acceleration meter/square second m/s2
angle radian rad
area square meter m2
capacitance farad F
density kilogram/cubic meter kg/m3
dynamic viscosity pascal second Pa-s
electric charge coulomb C
electric conductance siemens S
electric resistance ohm Ω
energy joule J
force newton N
frequency hertz Hz
inductance henry H
mass flow rate kilogram/second kg/s
mole flow rate mole/second mol/s
power watt W
pressure pascal Pa
speed meter/second m/s
surface tension newton/meter N/m
torque newton meter N-m
voltage volt V
volume cubic meter m3
volume flow rate cubic meter/second m3/s
amount-of-substance concentration mole/cubic meter mol/m3

non-SI units used on

Type Name Symbol
computer data storage byte B
computer data rate bit/second bit/s
U.S. currency dollar $

SI prefixes

Factor Prefix Symbol
1024 1E24 yotta Y
1021 1E21 zetta Z
1018 1E18 exa E
1015 1E15 peta P
1012 1E12 tera T
109 1E9 giga G
106 1E6 mega M
103 1E3 kilo k
102 1E2 hecto h
101 1E1 deca da
101 1E1 deka da
10-1 1E-1 deci d
10-2 1E-2 centi c
10-3 1E-3 milli m
10-6 1E-6 micro µ
10-9 1E-9 nano n
10-12 1E-12 pico p
10-15 1E-15 femto f
10-18 1E-18 atto a
10-21 1E-21 zepto z
10-24 1E-24 yocto y

International System of Units

The International System of Units (abbreviated SI) is the modern form of the metric system. It is the world's most widely used system of units, both in everyday commerce and in science.

The older metric system included several groupings of units. The SI was developed in 1960 from the metre-kilogram-second (mks) system, rather than the centimetre-gram-second (cgs) system which, in turn, had many variants.

The SI introduced several newly named units. The SI is not static; it is a living set of standards where units are created and definitions are modified with international agreement as measurement technology progresses.

With few exceptions, the system is used in every country in the world, and many countries do not maintain official definitions of other units. In the United States, industrial use of SI is increasing, but popular use is still limited. In the United Kingdom, conversion to metric units is official policy but not yet complete. Those countries that still recognize non-SI units (e.g. the U.S. and UK) have redefined their traditional non-SI units in terms of SI units.