List of international units

Last updated February 10, 2024

This list of international units is subsidiary to the list of units article and lists widely used modern units in a form of sortable table.

Unit system	Domain	Derivation	Unit name	Unit symbol	Dimension symbol	Quantity name	Definition	In SI base units	In other SI units
Unit system	Domain	Derivation	Unit name	Unit symbol	Dimension symbol	Quantity name	Definition	In SI base units	In other SI units	SI	Physics	Basic	second ^{[n 1]}	s	T	time	The duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.	s
SI	Physics	Basic	metre	m	L	length	The distance travelled by light in vacuum in 1/299792458 second.	m
SI	Physics	Basic	kilogram ^{[n 2]}	kg	M	mass	The kilogram is defined by setting the Planck constant $h$ exactly to 6.62607015×10⁻³⁴ J⋅s (J = kg⋅m²⋅s⁻²), given the definitions of the metre and the second.^[1]	kg
SI	Physics	Basic	ampere	A	I	electric current	The flow of exactly 1/1.602176634×10⁻¹⁹ times the elementary charge $e$ per second. Equalling approximately 6.2415090744×10¹⁸ elementary charges per second.	A
SI	Physics	Basic	kelvin	K	Θ	thermodynamic temperature	The kelvin is defined by setting the fixed numerical value of the Boltzmann constant $k$ to 1.380649×10⁻²³ J⋅K⁻¹, (J = kg⋅m²⋅s⁻²), given the definition of the kilogram, the metre, and the second.	K
SI	Physics	Basic	mole	mol	N	amount of substance	The amount of substance of exactly 6.02214076×10²³ elementary entities.^{[n 3]} This number is the fixed numerical value of the Avogadro constant, $N$ _A, when expressed in the unit mol⁻¹.	mol
SI	Physics	Basic	candela	cd	J	luminous intensity	The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 5.4×10¹⁴ hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.	cd
SI	Physics	Relational	radian ^{[n 4]}	rad		plane angle		m/m	1
SI	Physics	Relational	steradian	sr		solid angle		m²/m²	1
SI	Physics	Relational	hertz	Hz		frequency		s⁻¹
SI	Physics	Relational	newton	N		force		kg⋅m⋅s⁻²
SI	Physics	Relational	pascal	Pa		pressure		kg⋅m⁻¹⋅s⁻²	N/m²
SI	Physics	Relational	joule	J		energy, work, heat		kg⋅m²⋅s⁻²	N⋅m = Pa⋅m³
SI	Physics	Relational	watt	W		power, radiant flux		kg⋅m²⋅s⁻³	J/s
SI	Physics	Relational	coulomb	C		electric charge		s⋅A
SI	Physics	Relational	volt	V		electrical potential difference (voltage), emf		kg⋅m²⋅s⁻³⋅A⁻¹	W/A = J/C
SI	Physics	Relational	farad	F		capacitance		kg⁻¹⋅m⁻²⋅s⁴⋅A²	C/V
SI	Physics	Relational	ohm	Ω		resistance, impedance, reactance		kg⋅m²⋅s⁻³⋅A⁻²	V/A
SI	Physics	Relational	siemens	S		electrical conductance		kg⁻¹⋅m⁻²⋅s³⋅A²	Ω⁻¹
SI	Physics	Relational	weber	Wb		magnetic flux		kg⋅m²⋅s⁻²⋅A⁻¹	V⋅s
SI	Physics	Relational	tesla	T		magnetic flux density		kg⋅s⁻²⋅A⁻¹	Wb/m²
SI	Physics	Relational	henry	H		inductance		kg⋅m²⋅s⁻²⋅A⁻²	Wb/A
SI	Physics	Relational	degree Celsius	°C		temperature relative to 273.15 K		K
SI	Physics	Relational	lumen	lm		luminous flux		cd⋅sr
SI	Physics	Relational	lux	lx		illuminance		cd⋅sr⋅m⁻²	lm/m²
SI	Physics	Relational	becquerel	Bq		radioactivity (decays per unit time)		s⁻¹
SI	Physics	Relational	gray	Gy		absorbed dose (of ionising radiation)		m²⋅s⁻²	J/kg
SI	Physics	Relational	sievert	Sv		equivalent dose (of ionising radiation)		m²⋅s⁻²	J/kg
SI	Physics	Relational	katal	kat		catalytic activity		mol⋅s⁻¹
SI	Physics	Dimensional	square metre	m²	$A$	area
SI	Physics	Dimensional	cubic metre	m³	$V$	volume
SI	Physics	Relational	metre per second	m/s	$v$	speed, velocity
SI	Physics	Relational	metre per second squared	m/s²	$a$	acceleration
SI	Physics	Relational	reciprocal metre	m⁻¹	$σ$ , $ṽ$ or in optics $V$ , 1/ $f$	wavenumber, vergence (optics)
SI	Physics	Relational	kilogram per cubic metre	kg/m³	$ρ$	density
SI	Physics	Relational	kilogram per square metre	m⁻¹	$ρ$ _A	surface density
SI	Physics	Relational	cubic metre per kilogram	m³/kg	$v$	specific volume
SI	Physics	Relational	ampere per square metre	A/m²	$j$	current density
SI	Physics	Relational	ampere per metre	A/m	$H$	magnetic field strength
SI	Physics	Relational	mole per cubic metre	mol/m³	$c$	concentration
SI	Physics	Relational	kilogram per cubic metre	kg/m³	$ρ$ , $γ$	mass concentration
SI	Physics	Relational	candela per square metre	cd/m²	$L$ _v	luminance
?	Economics	Relational				velocity of money
?	Economics	Relational				gross margin

Notes

↑ Within the context of the SI, the second is the coherent base unit of time, and is used in the definitions of derived units. The name "second" historically arose as being the 2nd-levelsexagesimal division (1⁄60²) of some quantity, the hour in this case, which the SI classifies as an "accepted" unit along with its first-level sexagesimal division the minute.
↑ Despite the prefix "kilo-", the kilogram is the coherent base unit of mass, and is used in the definitions of derived units. Nonetheless, prefixes for the unit of mass are determined as if the gram were the base unit.
↑ When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.
↑ The radian and steradian are defined as dimensionless derived units.

↑ Materese, Robin (16 November 2018). "Historic Vote Ties Kilogram and Other Units to Natural Constants". NIST. Retrieved 16 November 2018.

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The kilogram is the base unit of mass in the International System of Units (SI), having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo colloquially. It means 'one thousand grams'.

<span class="mw-page-title-main">Litre</span> Unit of volume

The litre or liter 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 cubic decimetre occupies a volume of 10 cm × 10 cm × 10 cm and is thus equal to one-thousandth of a cubic metre.

The International System of Units, internationally known by the abbreviation SI, is the modern form of the metric system and the world's most widely used system of measurement. Coordinated by the International Bureau of Weights and Measures it is the only system of measurement with an official status in nearly every country in the world, employed in science, technology, industry, and everyday commerce.

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<span class="mw-page-title-main">Second</span> SI unit of time

The second is the unit of time in the International System of Units (SI), historically defined as 1⁄86400 of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each.

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 prefix kilo-, for example, may be added to gram to indicate multiplication by one thousand: one kilogram is equal to one thousand grams. The prefix milli-, likewise, may be added to metre to indicate division by one thousand; one millimetre is equal to one thousandth of a metre.

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<span class="mw-page-title-main">Metric time</span> Measure of time intervals using the metric system

Metric time is the measure of time intervals using the metric system. The modern SI system defines the second as the base unit of time, and forms multiples and submultiples with metric prefixes such as kiloseconds and milliseconds. Other units of time – minute, hour, and day – are accepted for use with SI, but are not part of it. Metric time is a measure of time intervals, while decimal time is a means of recording time of day.

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<span class="mw-page-title-main">Outline of the metric system</span> Overview of and topical guide to the metric system

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A coherent system of units is a system of units of measurement used to express physical quantities that are defined in such a way that the equations relating the numerical values expressed in the units of the system have exactly the same form, including numerical factors, as the corresponding equations directly relating the quantities. It is a system in which every quantity has a unique unit, or one that does not use conversion factors.

Since it's introduction in 1960, the base units for the International system of units, known as SI, have changed several times. Tables in this article summarize those changes.

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[1] Within the context of the SI, the second is the coherent base unit of time, and is used in the definitions of derived units. The name "second" historically arose as being the 2nd-levelsexagesimal division (1⁄60²) of some quantity, the hour in this case, which the SI classifies as an "accepted" unit along with its first-level sexagesimal division the minute.

[2] Despite the prefix "kilo-", the kilogram is the coherent base unit of mass, and is used in the definitions of derived units. Nonetheless, prefixes for the unit of mass are determined as if the gram were the base unit.

[4] When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.

[:0-5] The radian and steradian are defined as dimensionless derived units.

[NIST_2018-11-3] Materese, Robin (16 November 2018). "Historic Vote Ties Kilogram and Other Units to Natural Constants". NIST. Retrieved 16 November 2018.

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