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List of metric units

Metric units are units based on the metre, gram or second and decimal (power of ten) multiples or sub-multiples of these. According to Schadow and McDonald, metric units, in general, are those units "defined 'in the spirit' of the metric system, that emerged in late 18th century France and was rapidly adopted by scientists and engineers. Metric units are in general based on reproducible natural phenomena and are usually not part of a system of comparable units with different magnitudes, especially not if the ratios of these units are not powers of 10. Instead, metric units use multiplier prefixes that magnifies or diminishes the value of the unit by powers of ten." The most widely used examples are the units of the International System of Units (SI). By extension they include units of electromagnetism from the CGS and SI units systems, and other units for which use of SI prefixes has become the norm. Other unit systems using metric units include:

SI units

The first group of metric units are those that are at present defined as units within the International System of Units (SI). In its most restrictive interpretation, this is what may be meant when the term metric unit is used.

The unit one (1) is the unit of a quantity of dimension one. It is the neutral element of any system of units.

Furthermore, there are twenty-four metric prefixes that can be combined with any of these units except one (1) and kilogram (kg) to form further units of the SI. For mass, the same prefixes are applied to the gram (g) instead of the kilogram.

Non-SI metric units

There are several metric systems, most of which have become disused or are still used in only niche disciplines. Systems are listed with named units that are associated with them.

CGS

The centimetre–gram–second system of units (CGS) is based on three base units: centimetre, gram and second. Its subsystems (CGS-ESU, CGS-EMU and CGS-Gaussian) have different defining equations for their systems of quantities for defining electromagnetic quantities and hence the associated units, with CGS-Gaussian units being selected from each of the other two subsystems.

The CGS-to-SI correspondence of electromagnetic units as given was exact prior to the 2019 revision of the SI, until which the magnetic constant μ<sub>0</sub> was defined as . As from the redefinition, μ<sub>0</sub> has an inexactly known value when expressed in SI units, with the exactness of the electromagnetic unit correspondence given here being affected accordingly.

CGS nonelectromagnetic units

CGS-ESU electromagnetic units

CGS-EMU electromagnetic units

CGS-Gaussian electromagnetic units

MTS

MKS

MKpS units

Other metric units

Length

Area

  • The shed is a unit of area used in nuclear physics equal to 10<sup>−24</sup> barns (100&nbsp;rm<sup>2</sup> = 10<sup>−52</sup>&nbsp;m<sup>2</sup>).
  • The outhouse is a unit of area used in nuclear physics equal to 10<sup>−6</sup> barns (100 am<sup>2</sup> = 10<sup>−34</sup>&nbsp;m<sup>2</sup>).
  • The barn (b) is a unit of area used in nuclear physics equal to one hundred femtometres squared (100 fm<sup>2</sup> = 10<sup>−28</sup>&nbsp;m<sup>2</sup>).
  • The are (a) is a unit of area equal to .
  • The decare (daa) is a unit of area equal to .
  • The hectare (ha) is a unit of area equal to (0.01 km<sup>2</sup>).

Volume

  • The lambda (λ) is a unit of volume equal to one cubic millimetre (1&nbsp;mm<sup>3</sup>).
  • The litre (symbol l or L) is a unit of volume equal to one cubic decimetre (1&nbsp;dm<sup>3</sup>).
  • The stere (st) is a unit of volume equal to .

Reciprocal length

Time

  • The svedberg (S or Sv) is a unit of time used in chemistry equal to one hundred femtoseconds ().
  • The shake is a unit of time used in nuclear physics equal to ten nanoseconds ().
  • The sigma is a unit of time equal to one microsecond ().
  • The jiffy is sometimes used to mean a unit of time of .

Reciprocal time

Reciprocal time squared

Speed

  • The benz is a unit of speed equal to one metre per second (1&nbsp;m/s).

Acceleration

  • The leo is a unit of acceleration equal to .

Flow rate

  • The sverdrup (Sv) is a unit of volume flow rate equal to one million metres cubed per second (10<sup>6</sup> m<sup>3</sup>/s).

Mass

  • The undecimogramme is a unit of mass equal to ten picograms (10&nbsp;pg).
  • The gamma (γ) is a unit of mass equal to one microgram (1&nbsp;μg).
  • The gravet is a unit of mass equal to one gram (1&nbsp;g).
  • The grave is a unit of mass equal to one kilogram (1&nbsp;kg).
  • The bar is a unit of mass equal to one megagram (1&nbsp;Mg).

Linear mass density

Pressure

Energy

Viscosity

Electrical

Electromagnetic radiation

  • The jansky (Jy) is a unit of spectral irradiance equal to 10<sup>−26</sup>&nbsp;W⋅m<sup>−2</sup>⋅Hz<sup>−1</sup> ().
  • The solar flux unit is a unit of spectral irradiance equal to 10<sup>−22</sup>&nbsp;W⋅m<sup>−2</sup>⋅Hz<sup>−1</sup> ().
  • The nox (nx) is a unit of illuminance equal to 1&nbsp;millilux ().
  • The nit (nt) is a unit of luminance equal to one candela per metre squared ().
  • The lambert (L) is a unit of luminance equal to 10<sup>4</sup>/π&nbsp;cd⋅m<sup>−2</sup>.
  • The lumerg is a unit of luminous energy equal to lumen-seconds (100 nlm s).
  • The talbot (T) is a unit of luminous energy equal to one lumen-second ().
  • The einstein (E) has two conflicting definitions. The original is a unit of energy, equal to the energy in one mole (1 mol) of photons. The second is a unit of amount of photons, equal to one mole (1&nbsp;mol) of photons.
  • The rayleigh (R) is a unit of photon flux rate density equal to 10<sup>10</sup>&nbsp;m<sup>−2</sup>⋅s<sup>−1</sup> (10<sup>4</sup> mm<sup>−2</sup>⋅s<sup>−1</sup>).

Radioactivity

Concentration

  • The molar (M) is equal to one mole per litre ().

Acoustics

  • The acoustic ohm is a unit of acoustic impedance equal to 1 Pa·s/m<sup>3</sup>.

See also

Notes

References