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Metric prefixes in everyday use  

Text  Symbol  Factor  Power 
exa  E  000000000000000000 1  10^{18} 
peta  P  000000000000000 1  10^{15} 
tera  T  000000000000 1  10^{12} 
giga  G  000000000 1  10^{9} 
mega  M  000000 1  10^{6} 
kilo  k  000 1  10^{3} 
hecto  h  100  10^{2} 
deca  da  10  10^{1} 
(none)  (none)  1  10^{0} 
deci  d  0.1  10^{−1} 
centi  c  0.01  10^{−2} 
milli  m  0.001  10^{−3} 
micro  μ  001 0.000  10^{−6} 
nano  n  000001 0.000  10^{−9} 
pico  p  000000001 0.000  10^{−12} 
femto  f  000000000001 0.000  10^{−15} 
atto  a  000000000000001 0.000  10^{−18} 
Variants of the metric system  


The metric system is an internationally agreed decimal system of measurement. It was originally based on the mètre des Archives and the kilogramme des Archives introduced by the French First Republic in 1799, but over the years the definitions of the metre and the kilogram have been refined, and the metric system has been extended to incorporate many more units. Although a number of variants of the metric system emerged in the late nineteenth and early twentieth centuries, the term is now often used as a synonym for "SI" or the "International System of Units"—the official system of measurement in almost every country in the world.
The metric system has been officially sanctioned for use in the United States since 1866, but the US remains the only industrialised country that has not adopted the metric system as its official system of measurement: although In 1988, Congress passed the Omnibus Trade and Competitiveness Act, which designates "the metric system of measurement as the preferred system of weights and measures for United States trade and commerce". Among many other things, the act requires federal agencies to use metric measurements in nearly all of their activities, although there are still exceptions allowing traditional units to be used in documents intended for consumers. Many sources also cite Liberia and Myanmar as the only other countries not to have done so. Although the United Kingdom uses the metric system for most administrative and trade purposes, imperial units are widely used by the public and are permitted or obligatory for some purposes, such as road signs.
Although the originators intended to devise a system that was equally accessible to all, it proved necessary to use prototype units in the custody of national or local authorities as standards. Control of the prototype units of measure was maintained by the French government until 1875, when it was passed to an intergovernmental organisation, the General Conference on Weights and Measures (CGPM).
Quantity  CGS  MKS  MTS 

distance, displacement,

centimetre (cm)  metre (m)  metre 
mass (m)  gram (g)  kilogram (kg)  tonne (t) 
time (t)  second (s)  second  second 
speed, velocity (v, v)  cm/s  m/s  m/s 
acceleration (a)  gal (Gal)  m/s^{2}  m/s^{2} 
force (F)  dyne (dyn)  newton (N)  sthene (sn) 
pressure (P or p)  barye (Ba)  pascal (Pa)  pièze (pz) 
energy (E, Q, W)  erg (erg)  joule (J)  kilojoule (kJ) 
power (P)  erg/s  watt (W)  kilowatt (kW) 
viscosity (µ)  poise (p)  Pa·s  pz·s 
Quantity  Dimension  SI unit and symbol  Legacy unit and symbol  Conversion factor 

Time  T  second (s)  second (s)  1 
Length  L  metre (m) 
centimetre (cm) ångström (Å) 
0.01 10^{−10} 
Mass  M  kilogram (kg)  gram (g)  0.001 
Electric current  I  ampere (A) 
international ampere abampere or biot statampere 
022 1.000 10.0 641×10^{−10} 3.335 
Temperature  Θ 
kelvin (K) degree Celsius (°C) 
centigrade (°C)  [K] = [°C] + 273.15 1 
Luminous intensity  J  candela (cd)  international candle  0.982 
Amount of substance  N  mole (mol)  No legacy unit  n/a 
Area  L^{2}  square metre (m^{2})  are (are)  100 
Acceleration  LT^{−2}  (m·s^{−2})  gal (gal)  10^{−2} 
Frequency  T^{−1}  hertz (Hz)  cycles per second  1 
Energy  L^{2}MT^{−2}  joule (J)  erg (erg)  10^{−7} 
Power  L^{2}MT^{−3}  watt (W)  (erg/s) horsepower (HP) Pferdestärke (PS) 
10^{−7} 745.7 735.5 
Force  LMT^{−2}  newton (N) 
dyne (dyn) sthene (sn) kilopond (kp) 
10^{−5} 10^{3} 65 9.806 
Pressure  L^{−1}MT^{−2}  pascal (Pa) 
barye (Ba) pieze (pz) atmosphere (at) 
0.1 10^{3} 25×10^{5} 1.013 
Electric charge  IT  coulomb (C) 
abcoulomb statcoulomb or franklin 
10 641×10^{−10} 3.335 
Potential difference  L^{2}MT^{−3}I^{−1}  volt (V) 
international volt abvolt statvolt 
34 1.000 10^{−8} 925×10^{2} 2.997 
Capacitance  L^{−2}M^{−1}T^{4}I^{2}  farad (F)  abfarad statfarad 
10^{9} 650×10^{−12} 1.112 
Inductance  L^{2}MT^{−2}I^{−2}  henry (H) 
abhenry stathenry 
10^{−9} 552×10^{11} 8.987 
Electric resistance  L^{2}MT^{−3}I^{−2}  ohm (Ω)  international ohm abohm statohm 
49 1.000 10^{−9} 552×10^{11} 8.987 
Electric conductance  L^{−2}M^{−1}T^{3}I^{2}  siemens (S) 
international mho (℧) abmho statmho 
51 0.999 10^{9} 650×10^{−12} 1.112 
Magnetic flux  L^{2}MT^{−2}I^{−1}  weber (Wb)  maxwell (Mx)  10^{−8} 
Magnetic flux density  MT^{−2}I^{−1}  tesla (T)  gauss (G)  10^{−4} 
Magnetic field strength  IL^{−1}  (A/m)  oersted (Oe)  ^{103}⁄_{4π} = 47 79.577 
Dynamic viscosity  ML^{−1}T^{−1}  (Pa·s)  poise (P)  0.1 
Kinematic viscosity  L^{2}T^{−1}  (m^{2}·s^{−1})  stokes (St)  10^{−4} 
Luminous flux  J  lumen (lm)  stilb (sb)  10^{4} 
Illuminance  JL^{−2}  lux (lx)  phot (ph)  10^{4} 
[Radioactive] activity  T^{−1}  becquerel (Bq)  curie (Ci)  ×10^{10} 3.70 
Absorbed [radiation] dose  L^{2}T^{−2}  gray (Gy) 
roentgen (R) rad (rad) 
≈0.01 0.01 
Radiation dose equivalent  L^{2}T^{−2}  sievert  roentgen equivalent man (rem)  0.01 
Catalytic activity  NT^{−1}  katal (kat)  No legacy unit  n/a 
Quantity  Dimension  Unit and symbol  Equivalence 

Mass  M  tonne (t)  1000 kg 
Area  L^{2}  hectare (ha)  0.01 km^{2} 10^{4} m^{2} 
Volume  L^{3}  litre (L or l)  0.001 m^{3} 
Time  T 
minute (min) hour (h) day (d) 
60 s 3600 s 400 s 86 
Pressure  L^{−1}MT^{−2}  bar  100 kPa 
Plane angle  none 
degree (°) minute (ʹ) second (″) 
( ^{π}⁄_{180}) rad ( ^{π}⁄_{7004108000000000000♠10800}) rad ( ^{π}⁄_{7005648000000000000♠648000}) rad 
1 mm^{2} (square millimetre)  = (1 mm)^{2}  = (0.001 m)^{2}  = 001 m^{2} 0.000 
1 km^{2} (square kilometre)  = (1 km)^{2}  = (1000 m)^{2}  = 000000 m^{2} 1 
1 mm^{3} (cubic millimetre)  = (1 mm)^{3}  = (0.001 m)^{3}  = 000001 m^{3} 0.000 
1 km^{3} (cubic kilometre)  = (1 km)^{3}  = (1000 m)^{3}  = 000000000 m^{3} 1 
force  = mass  × acceleration 
energy  = force  × distance 
power  = energy  ÷ time 
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