›› SI base units used on ConvertUnits.com

 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 ConvertUnits.com

 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 ConvertUnits.com

 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.