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 The International System of Units, internationally known by the abbreviation SI (from French ), is the modern form of the metric system and the world's most widely used system of measurement. It is the only system of measurement with official s ...

(SI). By extension they include units of

electromagnetism In physics, electromagnetism is an interaction that occurs between particles with electric charge via electromagnetic fields. The electromagnetic force is one of the four fundamental forces of nature. It is the dominant force in the interacti ...

from the CGS and SI units systems, and other units for which use of

SI prefix The International System of Units, internationally known by the abbreviation SI (from French ), is the modern form of the metric system and the world's most widely used system of measurement. It is the only system of measurement with official st ...

es has become the norm. Other unit systems using metric units include: * International System of Electrical and Magnetic Units * Metre–tonne–second (MTS) system of units *

MKS system of units The metre, kilogram, second system of units, also known more briefly as MKS units or the MKS system, is a physical system of measurement based on the metre, kilogram, and second (MKS) as base units. Distances are described in terms of metres, mass ...

(metre, kilogram, second)

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 prefix A metric prefix is a unit prefix that precedes a basic unit of measure to indicate a multiple or submultiple of the unit. All metric prefixes used today are decadic. Each prefix has a unique symbol that is prepended to any unit symbol. The pr ...

es'' 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 The centimetre–gram–second system of units (CGS or cgs) is a variant of the metric system based on the centimetre as the unit of length, the gram as the unit of mass, and the second as the unit of time. All CGS mechanical units are unamb ...

(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''₀ was defined as . As from the redefinition, ''μ''₀ 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

* The kayser (K) is a unit of

wavenumber In the physical sciences, the wavenumber (or wave number), also known as repetency, is the spatial frequency of a wave. Ordinary wavenumber is defined as the number of wave cycles divided by length; it is a physical quantity with dimension of ...

equal to (). * The gal (Gal) is a unit of

acceleration In mechanics, acceleration is the Rate (mathematics), rate of change of the velocity of an object with respect to time. Acceleration is one of several components of kinematics, the study of motion. Accelerations are Euclidean vector, vector ...

equal to . * The

dyne The dyne (symbol: dyn; ) is a derived units of measurement, unit of force (physics), force specified in the centimetre–gram–second system of units, centimetre–gram–second (CGS) system of units, a predecessor of the modern International S ...

(dyn) is a unit of

force In physics, a force is an influence that can cause an Physical object, object to change its velocity unless counterbalanced by other forces. In mechanics, force makes ideas like 'pushing' or 'pulling' mathematically precise. Because the Magnitu ...

equal to (). * The barye (Ba) is a unit of

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and eve ...

equal to (). * The erg (erg) is a unit of

energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

equal to (). * The poise (P) is a unit of dynamic viscosity equal to (). * The stokes (St) is a unit of kinematic viscosity equal to (). * The stilb (sb) is a unit of luminance equal to (). * The phot (ph) is a unit of

illuminance In photometry (optics), photometry, illuminance is the total luminous flux incident on a surface, per unit area. It is a measure of how much the incident light illuminates the surface, wavelength-weighted by the luminosity function to correlate ...

equal to (). * The rayl is a unit of specific acoustic impedance, equal to 1 dyn⋅s⋅cm⁻³ (10 Pa s/m).

CGS-ESU electromagnetic units

* The statwatt (statW) is a unit of power equal to , which is equal to . * The statcoulomb (statC) or franklin (Fr) is a unit of

electric charge Electric charge (symbol ''q'', sometimes ''Q'') is a physical property of matter that causes it to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative''. Like charges repel each other and ...

equal to , corresponding to ~. * The statampere (statA) is a unit of

electric current An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...

equal to , corresponding to ~. * The statvolt (statV) is a unit of electric potential difference equal to , corresponding to . * The statohm is a unit of electric resistance equal to , corresponding to ~. * The statsiemens or statmho is a unit of electric conductance equal to , corresponding to ~. * The stathenry is a unit of electric inductance equal to , corresponding to ~. * The statfarad (statF) is a unit of electric capacitance equal to , corresponding to ~. * The statdaraf (statD) is a unit of electric elastance equal to 1/statF. * The statweber is a unit of magnetic flux, corresponding to . * The stattesla is a unit of magnetic flux density equal to , corresponding to .

CGS-EMU electromagnetic units

* The abwatt (abW) is a unit of power equal to , which is equal to . * The abcoulomb (abC) is a unit of

equal to , corresponding to . * The abampere (abA) or biot (Bi) is a unit of

, corresponding to . * The abvolt (abV) is a unit of electric potential difference, corresponding to . * The abohm (abΩ) is a unit of electric resistance, corresponding to . * The abmho is a unit of electric conductance, corresponding to . * The abhenry is a unit of electric inductance, corresponding to . * The abfarad (abF) is a unit of electric capacitance, corresponding to . * The gilbert (Gb) is a unit of magnetomotive force equal to one biot-turn, corresponding to (10/4π) A = . * The oersted (Oe) is a unit of magnetic field strength equal to , corresponding to (1000/4π) A/m = . * The

maxwell Maxwell may refer to: People * Maxwell (surname), including a list of people and fictional characters with the name ** James Clerk Maxwell, mathematician and physicist * Justice Maxwell (disambiguation) * Maxwell baronets, in the Baronetage of N ...

(Mx) is a unit of magnetic flux, corresponding to . * The

gauss Johann Carl Friedrich Gauss (; ; ; 30 April 177723 February 1855) was a German mathematician, astronomer, Geodesy, geodesist, and physicist, who contributed to many fields in mathematics and science. He was director of the Göttingen Observat ...

(G) is a unit of magnetic flux density, corresponding to .

CGS-Gaussian electromagnetic units

* The franklin (Fr) is a unit of

equal to , corresponding to ~. * The oersted (Oe) is a unit of magnetic field strength equal to , corresponding to ~. * The

(Mx) is a unit of magnetic flux, corresponding to . * The

(G) is a unit of magnetic flux density, corresponding to .

MTS

* The

tonne The tonne ( or ; symbol: t) is a unit of mass equal to 1,000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton in the United States to distinguish it from the non-metric units of the s ...

(t) is a unit of

mass Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...

equal to . * The sthène (sn) is a unit of

equal to . * The pièze (pz) is a unit of

equal to .

MKS

* The

cycle per second The cycle per second is a once-common English name for the unit of frequency now known as the ''hertz'' (Hz). Cycles per second may be denoted by c.p.s., c/s, or, ambiguously, just "cycles" (Cyc., Cy., C, or c). The term comes from repetitive p ...

(cps or cyc/s) is a unit of

frequency Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...

equal to . * The MKS rayl is a unit of

acoustic impedance Acoustic impedance and specific acoustic impedance are measures of the opposition that a system presents to the acoustic flow resulting from an acoustic pressure applied to the system. The International System of Units, SI unit of acoustic impeda ...

equal to . * The mho (℧) is a unit of electric conductance equal to .

MKpS units

* The

kilogram-force The kilogram-force (kgf or kgF), or kilopond (kp, from ), is a non-standard Gravitational metric system, gravitational metric unit of force. It is not accepted for use with the International System of Units (SI) and is deprecated for most uses. T ...

(kgf), also kilopond (kp), is a unit of

(). * The hyl is a unit of

equal to (). * The poncelet (p) is a unit of power equal to (). * The technical atmosphere (at) is a (non-coherent) unit of

equal to ().

Other metric units

Length

* The fermi is a unit of distance used in

nuclear physics Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions, in addition to the study of other forms of nuclear matter. Nuclear physics should not be confused with atomic physics, which studies th ...

equal to . * The angstrom (symbol Å) is a unit of distance used in

chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...

and

atomic physics Atomic physics is the field of physics that studies atoms as an isolated system of electrons and an atomic nucleus. Atomic physics typically refers to the study of atomic structure and the interaction between atoms. It is primarily concerned wit ...

equal to . * The micron (μ) is a unit of distance equal to one

micrometre The micrometre (English in the Commonwealth of Nations, Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a uni ...

(). * The basic module (M) is a unit of distance equal to one hundred millimetres (). * The myriametre (mym) is a unit of distance equal to ten kilometres (). * The hebdometre is a unit of distance equal to ten megametres (). * The spat (S) is a unit of distance equal to one terametre ().

Area

* The

shed A shed is typically a simple, single-storey (though some sheds may have two or more stories and or a loft) roofed structure, often used for storage, for hobby, hobbies, or as a workshop, and typically serving as outbuilding, such as in a bac ...

is a unit of area used in nuclear physics equal to 10⁻²⁴ barns (100 rm² = 10⁻⁵² m²). * The outhouse is a unit of area used in nuclear physics equal to 10⁻⁶ barns (100 am² = 10⁻³⁴ m²). * The barn (b) is a unit of area used in nuclear physics equal to one hundred femtometres squared (100 fm² = 10⁻²⁸ m²). * The are (a) is a unit of area equal to . * The decare (daa) is a unit of area equal to . * The

hectare The hectare (; SI symbol: ha) is a non-SI metric unit of area equal to a square with 100-metre sides (1 hm2), that is, square metres (), and is primarily used in the measurement of land. There are 100 hectares in one square kilometre. ...

(ha) is a unit of area equal to (0.01 km²).

Volume

* The

lambda Lambda (; uppercase , lowercase ; , ''lám(b)da'') is the eleventh letter of the Greek alphabet, representing the voiced alveolar lateral approximant . In the system of Greek numerals, lambda has a value of 30. Lambda is derived from the Phoen ...

(λ) is a unit of volume equal to one cubic

millimetre 330px, Different lengths as in respect of the electromagnetic spectrum, measured by the metre and its derived scales. The microwave is between 1 metre to 1 millimetre. The millimetre (American and British English spelling differences#-re, -er, i ...

(1 mm³). * The

litre The litre ( Commonwealth spelling) or liter ( American spelling) (SI symbols L and l, other symbol used: ℓ) is a metric unit of volume. It is equal to 1 cubic decimetre (dm3), 1000 cubic centimetres (cm3) or 0.001 cubic metres (m3). A ...

(symbol l or L) is a unit of volume equal to one cubic decimetre (1 dm³). * The stere (st) is a unit of volume equal to .

Reciprocal length

* The dioptre is a unit of

optical power In optics, optical power (also referred to as dioptric power, refractive power, focal power, focusing power, or convergence power) is the degree to which a lens, mirror, or other optical system converges or diverges light. It is equal to the ...

equal to one reciprocal metre ().

Time

* The

svedberg In chemistry, a Svedberg unit or svedberg (symbol S, sometimes Sv) is a non- SI metric unit for sedimentation coefficients. The Svedberg unit offers a measure of a particle's size indirectly based on its sedimentation rate under acceleration ...

(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 Sigma ( ; uppercase Σ, lowercase σ, lowercase in word-final position ς; ) is the eighteenth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 200. In general mathematics, uppercase Σ is used as an operator ...

is a unit of time equal to one

microsecond A microsecond is a unit of time in the International System of Units (SI) equal to one millionth (0.000001 or 10−6 or ) of a second. Its symbol is μs, sometimes simplified to us when Unicode is not available. A microsecond is to one second, ...

(). * The jiffy is sometimes used to mean a unit of time of .

Reciprocal time

* The fresnel is a unit of

equal to .

Reciprocal time squared

* The eotvos (E) is a unit of gravitational gradient equal to ().

Speed

* The benz is a unit of

speed In kinematics, the speed (commonly referred to as ''v'') of an object is the magnitude of the change of its position over time or the magnitude of the change of its position per unit of time; it is thus a non-negative scalar quantity. Intro ...

equal to one metre per second (1 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 (10⁶ m³/s).Aldersey-Williams, 2016
/ref>

Mass

* The undecimogramme is a unit of

equal to ten picograms (10 pg). * The

gamma Gamma (; uppercase , lowercase ; ) is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3. In Ancient Greek, the letter gamma represented a voiced velar stop . In Modern Greek, this letter normally repr ...

(γ) is a unit of

equal to one microgram (1 μg). * The gravet is a unit of

equal to one gram (1 g). * The

grave A grave is a location where a cadaver, dead body (typically that of a human, although sometimes that of an animal) is burial, buried or interred after a funeral. Graves are usually located in special areas set aside for the purpose of buria ...

is a unit of

equal to one kilogram (1 kg). * The bar is a unit of

equal to one megagram (1 Mg).

Linear mass density

* The

tex Tex, TeX, TEX, may refer to: People and fictional characters * Tex (nickname), a list of people and fictional characters with the nickname * Tex Earnhardt (1930–2020), U.S. businessman * Joe Tex (1933–1982), stage name of American soul singer ...

(tex) is a unit of linear mass density equal to one gram per kilometre (1 g/km). * The number metric (Nm) is equal to 1000 metres per kilogram (1 km/kg).

Pressure

* The

metre sea water The metre (or meter) sea water (msw) is a metric unit of pressure used in underwater diving Underwater diving, as a human activity, is the practice of descending below the water's surface to interact with the environment. It is also o ...

(msw) is a unit of

defined as 0.1 bar, which is equal to . * The bar (bar) is a unit of

equal to .

Energy

* The foe is a unit of

equal to ().

Viscosity

* The poiseuille is a unit of dynamic viscosity equal to one pascal-second ().

Electrical

* The Siemens mercury unit is a unit of electric resistance, corresponding to ~. * The gamma (γ) a unit of magnetic flux density, corresponding to . * The debye (D) is a unit of electric dipole moment equal to , corresponding to ~. * The

buckingham Buckingham ( ) is a market town in north Buckinghamshire, England, close to the borders of Northamptonshire and Oxfordshire, which had a population of 12,890 at the United Kingdom Census 2011, 2011 Census. The town lies approximately west of ...

(B) is a unit of electric quadrupole moment equal to .

Electromagnetic radiation

* The jansky (Jy) is a unit of spectral irradiance equal to 10⁻²⁶ W⋅m⁻²⋅Hz⁻¹ (). * The solar flux unit is a unit of spectral irradiance equal to 10⁻²² W⋅m⁻²⋅Hz⁻¹ (). * The nox (nx) is a unit of

equal to 1 millilux (). * The nit (nt) is a unit of luminance equal to one

candela The candela (symbol: cd) is the unit of luminous intensity in the International System of Units (SI). It measures luminous power per unit solid angle emitted by a light source in a particular direction. Luminous intensity is analogous to radi ...

per metre squared (). * The lambert (L) is a unit of luminance equal to 10⁴/π cd⋅m⁻². * 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

, equal to the energy in one mole (1 mol) of photons. The second is a unit of amount of

photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that can ...

s, equal to one mole (1 mol) of photons. * The rayleigh (R) is a unit of photon flux rate density equal to 10¹⁰ m⁻²⋅s⁻¹ (10⁴ mm⁻²⋅s⁻¹).

Radioactivity

* The rad (rad) is a unit of absorbed dose equal to . * The roentgen equivalent man (rem) is a unit of equivalent dose equal to . * The rutherford (Rd) is a unit of

radioactivity Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

defined as one million decays per second ().

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/m³.

Notes

References

{{Reflist Metric system Metric

SI units

Non-SI metric units

CGS

CGS nonelectromagnetic units

CGS-ESU electromagnetic units

CGS-EMU electromagnetic units

CGS-Gaussian electromagnetic units

MTS

MKS

MKpS units

Other metric units

Length

Area

Volume

Reciprocal length

Time

Reciprocal time

Reciprocal time squared

Speed

Acceleration

Flow rate

Mass

Linear mass density

Pressure

Energy

Viscosity

Electrical

Electromagnetic radiation

Radioactivity

Concentration

Acoustics

See also

Notes

References