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Metric System
Metric System
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 Quantity CGS MKS MTS distance, displacement,  length, height, etc.
 (d, x, l, h, etc.)
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
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,  length, height, etc.
 (d, x, l, h, etc.)
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
factorTime 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
statampere022 1.000
10.0
641×10^{−10} 3.335Temperature Θ kelvin (K)
degree Celsius (°C)centigrade (°C) [K] = [°C] + 273.15
1Luminous 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
735.5Force LMT^{−2} newton (N) dyne (dyn)
sthene (sn)
kilopond (kp)10^{−5}
10^{3}
65 9.806Pressure L^{−1}MT^{−2} pascal (Pa) barye (Ba)
pieze (pz)
atmosphere (at)0.1
10^{3}
25×10^{5} 1.013Electric charge IT coulomb (C) abcoulomb
statcoulomb or franklin10
641×10^{−10} 3.335Potential difference L^{2}MT^{−3}I^{−1} volt (V) international volt
abvolt
statvolt34 1.000
10^{−8}
925×10^{2} 2.997Capacitance L^{−2}M^{−1}T^{4}I^{2} farad (F) abfarad
statfarad10^{9}
650×10^{−12} 1.112Inductance L^{2}MT^{−2}I^{−2} henry (H) abhenry
stathenry10^{−9}
552×10^{11} 8.987Electric resistance L^{2}MT^{−3}I^{−2} ohm (Ω) international ohm
abohm
statohm49 1.000
10^{−9}
552×10^{11} 8.987Electric conductance L^{−2}M^{−1}T^{3}I^{2} siemens (S) international mho (℧)
abmho
statmho51 0.999
10^{9}
650×10^{−12} 1.112Magnetic 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
0.01Radiation 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 86Pressure 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 mg = 0.001 g
 1 km = 1000 m

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
 length, height, etc.
 (d, x, l, h, etc.)
 The mètre for length
 The are (100 m^{2}) for area [of land]
 The stère (1 m^{3}) for volume of stacked firewood
 The litre (1 dm^{3}) for volumes of liquid
 The gramme for mass.
 General Conference on Weights and Measures (CGPM), an intergovernmental conference of official delegates of member nations and the supreme authority for all actions;
 International Committee for Weights and Measures (CIPM), consisting of selected scientists and metrologists, which prepares and executes the decisions of the CGPM and is responsible for the supervision of the International Bureau of Weights and Measures (BIPM);
 International Bureau of Weights and Measures (BIPM), a permanent laboratory and world centre of scientific metrology, the activities of which include the establishment of the basic standards and scales of the principal physical quantities and maintenance of the international prototype standards.
 NonSI units accepted for use with the International System of Units (Table 6). This list includes the hour and minute, the angular measures (degree, minute and second of arc) and the historic [noncoherent] metric units, the litre, tonne and hectare (originally agreed by the CGPM in 1879)
 NonSI units whose values in SI units must be obtained experimentally (Table 7). This list includes various units of measure used in atomic and nuclear physics and in astronomy such as the dalton, the electron mass, the electron volt, the astronomical unit, the solar mass, and a number of other units of measure that are wellestablished, but dependent on experimentallydetermined physical quantities.
 Other nonSI units (Table 8). This list catalogues a number of units of measure that have been used internationally in certain welldefined spheres including the bar for pressure, the ångström for atomic physics, the nautical mile and the knot in navigation.
 NonSI units associated with the CGS and the CGSGaussian system of units (Table 9). This table catalogues a number of units of measure based on the CGS system and dating from the nineteenth century. They appear frequently in the literature, but their continued use is discouraged by the CGPM.
 Flying an overloaded American International Airways aircraft from Miami, Florida to Maiquetia, Venezuela on 26 May 1994. The degree of overloading was consistent with ground crew reading the kilogram markings on the cargo as pounds.
 In 1999 the Institute for Safe Medication Practices reported that confusion between grains and grams led to a patient receiving phenobarbital 0.5 grams instead of 0.5 grains (0.03 grams) after the practitioner misread the prescription.
 The Canadian "Gimli Glider" accident in 1983, when a Boeing 767 jet ran out of fuel in midflight because of two mistakes made when calculating the fuel supply of Air Canada's first aircraft to use metric measurements: mechanics miscalculated the amount of fuel required by the aircraft as a result of their unfamiliarity with metric units.
 The root cause of the loss in 1999 of NASA's US$125 million Mars Climate Orbiter was a mismatch of units – the spacecraft engineers calculated the thrust forces required for velocity changes using US customary units (lbf·s) whereas the team who built the thrusters were expecting a value in metric units (N·s) as per the agreed specification.
 in addition to the speed of light, define four constants of nature—Planck's constant, an elementary charge, Boltzmann constant and Avogadro constant – to have exact values
 retire the international prototype kilogram
 revise the current definitions of the kilogram, ampere, kelvin and mole to make use of the above four constants of nature
 tighten the wording of the definitions of all the base units
 Binary prefix, used in computer science
 Conversion of units
 History of measurement
 ISO/IEC 80000, style manual for measurements metric and nonmetric, superseding ISO 31
 Metrication, the process of introducing the SI metric system as the worldwide standard for physical measurements
 Metrology
 Units of measurement
 CBC Radio Archives For Good Measure: Canada Converts to Metric
 U.S. Metric Association Metrication in other countries
What Else?
Metric System