Non-SI units accepted for use with SI

This is a list of units that are not defined as part of the International System of Units

International System of Units

The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

(SI), but are otherwise mentioned in the SI, because either the General Conference on Weights and Measures (CGPM)

General Conference on Weights and Measures

The General Conference on Weights and Measures is the English name of the Conférence générale des poids et mesures . It is one of the three organizations established to maintain the International System of Units under the terms of the Convention du Mètre of 1875...

accepts their use as being multiples or submultiples of SI-units, they have important contemporary application worldwide, or are otherwise commonly encountered worldwide.

Units officially accepted for use with the SI

Name	Symbol	Quantity	Equivalent SI unit
Widely used units expected to be used indefinitely
minute Minute A minute is a unit of measurement of time or of angle. The minute is a unit of time equal to 1/60th of an hour or 60 seconds. In the UTC time scale, a minute on rare occasions has 59 or 61 seconds; see leap second. The minute is not an SI unit; however, it is accepted for use with SI units...	min	time Time Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects.... (SI unit multiple)	1 min = 60 s Second The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....
hour Hour The hour is a unit of measurement of time. In modern usage, an hour comprises 60 minutes, or 3,600 seconds...	h	time (SI unit multiple)	1 h = 60 min = 3600 s
day Day A day is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean that portion of the full day during which a location is illuminated by the light of the sun...	d	time (SI unit multiple)	1 d = 24 h = 1440 min = 86400 s
degree Degree (angle) A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...	°	plane angle Angle In geometry, an angle is the figure formed by two rays sharing a common endpoint, called the vertex of the angle.Angles are usually presumed to be in a Euclidean plane with the circle taken for standard with regard to direction. In fact, an angle is frequently viewed as a measure of an circular arc... (dimensionless unit)	1° = (π / 180) rad Radian Radian is the ratio between the length of an arc and its radius. The radian is the standard unit of angular measure, used in many areas of mathematics. The unit was formerly a SI supplementary unit, but this category was abolished in 1995 and the radian is now considered a SI derived unit...
minute Minute of arc A minute of arc, arcminute, or minute of angle , is a unit of angular measurement equal to one sixtieth of one degree. In turn, a second of arc or arcsecond is one sixtieth of one minute of arc....	′	plane angle (dimensionless unit)	1′ = (1 / 60)° = (π / 10800) rad
second	″	plane angle (dimensionless unit)	1″ = (1 / 60)′ = (1 / 3600)° = (π / 648000) rad
hectare Hectare The hectare is a metric unit of area defined as 10,000 square metres , and primarily used in the measurement of land. In 1795, when the metric system was introduced, the are was defined as being 100 square metres and the hectare was thus 100 ares or 1/100 km2...	ha	area Area Area is a quantity that expresses the extent of a two-dimensional surface or shape in the plane. Area can be understood as the amount of material with a given thickness that would be necessary to fashion a model of the shape, or the amount of paint necessary to cover the surface with a single coat... (decimal unit multiple)	1 ha = 100 a = 10000 m² = 1 hm²
litre Litre pic\|200px\|right\|thumb\|One litre is equivalent to this cubeEach side is 10 cm1 litre water = 1 kilogram water The litre is a metric system unit of volume equal to 1 cubic decimetre , to 1,000 cubic centimetres , and to 1/1,000 cubic metre...	l or L	volume Volume Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains.... (decimal unit multiple)	1 L = 1 dm³ = 0.001 m³ Cubic metre The cubic metre is the SI derived unit of volume. It is the volume of a cube with edges one metre in length. An alternative name, which allowed a different usage with metric prefixes, was the stère... = 1000 cc Cubic centimetre A cubic centimetre is a commonly used unit of volume extending the derived SI-unit cubic metre, and corresponds to the volume of a cube measuring 1 cm × 1 cm × 1 cm... = 1000 cm Centimetre A centimetre is a unit of length in the metric system, equal to one hundredth of a metre, which is the SI base unit of length. Centi is the SI prefix for a factor of . Hence a centimetre can be written as or — meaning or respectively... ³
tonne Tonne The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...	t	mass Mass Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:... (decimal unit multiple)	1 t = 10³ kg Kilogram The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water... = 1 Mg
Logarithmic units
neper Neper The neper is a logarithmic unit for ratios of measurements of physical field and power quantities, such as gain and loss of electronic signals. It has the unit symbol Np. The unit's name is derived from the name of John Napier, the inventor of logarithms...	Np	dimensionless ratio Ratio In mathematics, a ratio is a relationship between two numbers of the same kind , usually expressed as "a to b" or a:b, sometimes expressed arithmetically as a dimensionless quotient of the two which explicitly indicates how many times the first number contains the second In mathematics, a ratio is... of field quantities	L_F = ln(F / F₀) Np
		dimensionless ratio of power quantities	L_P = ln(P / P₀) Np
bel, decibel Decibel The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...	B, dB	dimensionless ratio Ratio In mathematics, a ratio is a relationship between two numbers of the same kind , usually expressed as "a to b" or a:b, sometimes expressed arithmetically as a dimensionless quotient of the two which explicitly indicates how many times the first number contains the second In mathematics, a ratio is... of field quantities	L_F = 2 log₁₀(F / F₀) B
		dimensionless ratio of power quantities	L_P = log₁₀(P / P₀) B
Units with experimentally determined values
electron-volt	eV	energy Energy In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...	1 eV =
atomic mass unit Atomic mass unit The unified atomic mass unit or dalton is a unit that is used for indicating mass on an atomic or molecular scale. It is defined as one twelfth of the rest mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state, and has a value of... dalton	u Da	mass Mass Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...	1 u = 1 Da =
astronomical unit Astronomical unit An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....	ua	length Length In geometric measurements, length most commonly refers to the longest dimension of an object.In certain contexts, the term "length" is reserved for a certain dimension of an object along which the length is measured. For example it is possible to cut a length of a wire which is shorter than wire...	1 ua =
Natural units (n.u.)
speed of light Speed of light The speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...	c₀	speed Speed In kinematics, the speed of an object is the magnitude of its velocity ; it is thus a scalar quantity. The average speed of an object in an interval of time is the distance traveled by the object divided by the duration of the interval; the instantaneous speed is the limit of the average speed as...	(exact)
reduced Planck constant	ħ	action Action (physics) In physics, action is an attribute of the dynamics of a physical system. It is a mathematical functional which takes the trajectory, also called path or history, of the system as its argument and has a real number as its result. Action has the dimension of energy × time, and its unit is...	J·s
electron rest mass Electron rest mass The electron rest mass is the mass of a stationary electron. It is one of the fundamental constants of physics, and is also very important in chemistry because of its relation to the Avogadro constant...	m_e	mass Mass Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
n.u. of time		time Time Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....
Atomic units (a.u.)
elementary charge Elementary charge The elementary charge, usually denoted as e, is the electric charge carried by a single proton, or equivalently, the absolute value of the electric charge carried by a single electron. This elementary charge is a fundamental physical constant. To avoid confusion over its sign, e is sometimes called...	e	electric charge Electric charge Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
Bohr radius Bohr radius The Bohr radius is a physical constant, approximately equal to the most probable distance between the proton and electron in a hydrogen atom in its ground state. It is named after Niels Bohr, due to its role in the Bohr model of an atom...	a₀	length Length In geometric measurements, length most commonly refers to the longest dimension of an object.In certain contexts, the term "length" is reserved for a certain dimension of an object along which the length is measured. For example it is possible to cut a length of a wire which is shorter than wire...
Hartree energy Hartree energy The hartree , also known as the Hartree energy, is the atomic unit of energy, named after the British physicist Douglas Hartree. It is defined as...	E_h	energy Energy In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
a.u. of time	ħ / E_h	time Time Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

Common units not officially sanctioned

Name	Symbol	Quantity	Equivalent SI unit
Ångström Ångström The angstrom or ångström, is a unit of length equal to 1/10,000,000,000 of a meter . Its symbol is the Swedish letter Å.... , angstrom	Å	length	1 Å = 0.1 nm = 10⁻¹⁰ m Metre The metre , symbol m, is the base unit of length in the International System of Units . Originally intended to be one ten-millionth of the distance from the Earth's equator to the North Pole , its definition has been periodically refined to reflect growing knowledge of metrology...
nautical mile Nautical mile The nautical mile is a unit of length that is about one minute of arc of latitude along any meridian, but is approximately one minute of arc of longitude only at the equator...	nm	length Length In geometric measurements, length most commonly refers to the longest dimension of an object.In certain contexts, the term "length" is reserved for a certain dimension of an object along which the length is measured. For example it is possible to cut a length of a wire which is shorter than wire...	1 nautical mile = 1852 m Metre The metre , symbol m, is the base unit of length in the International System of Units . Originally intended to be one ten-millionth of the distance from the Earth's equator to the North Pole , its definition has been periodically refined to reflect growing knowledge of metrology...
knot	kt	speed Speed In kinematics, the speed of an object is the magnitude of its velocity ; it is thus a scalar quantity. The average speed of an object in an interval of time is the distance traveled by the object divided by the duration of the interval; the instantaneous speed is the limit of the average speed as...	1 knot = 1 nautical mile per hour = (1852 / 3600) m / s Metre per second Metre per second is an SI derived unit of both speed and velocity , defined by distance in metres divided by time in seconds....
are Hectare The hectare is a metric unit of area defined as 10,000 square metres , and primarily used in the measurement of land. In 1795, when the metric system was introduced, the are was defined as being 100 square metres and the hectare was thus 100 ares or 1/100 km2...	a	area	1 a = 1 dam² = 100 m² Square metre The square metre or square meter is the SI derived unit of area, with symbol m2 . It is defined as the area of a square whose sides measure exactly one metre...
barn Barn (unit) A barn is a unit of area. Originally used in nuclear physics for expressing the cross sectional area of nuclei and nuclear reactions, today it is used in all fields of high energy physics to express the cross sections of any scattering process, and is best understood as a measure of the...	b	area	1 b = 10⁻²⁸ m²
bar Bar (unit) The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...	bar	pressure Pressure Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...	1 bar = 10⁵ Pa Pascal (unit) The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...
millibar Bar (unit) The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...	mbar	pressure Pressure Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...	1 mbar = 1 hPa HPA -Organizations:Halifax Port Authority, a port authority in CanadaHamburg Port Authority, the port authority for the Port of Hamburg, Germany*Health Protection Agency, a health organization in the United Kingdom... = 100 Pa
atmosphere Atmosphere (unit) The standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of pressure. For practical purposes it has been replaced by the bar which is 105 Pa...	atm	pressure Pressure Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...	1 atm = 1013.25 mbar = 1013.25 hPa = exactly (commonly used in atmospheric meteorology, in oceanology and for pressures within liquids, or in the industry for pressures within containers of liquified gas)
dyne Dyne In physics, the dyne is a unit of force specified in the centimetre-gram-second system of units, a predecessor of the modern SI. One dyne is equal to exactly 10 µN... per square centimeter (barye Barye The barye , or sometimes barad, barrie, bary, baryd, baryed, or barie, is the centimetre-gram-second unit of pressure. It is equal to 1 dyne per square centimetre.... )	Ba	pressure Pressure Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...	1 Ba = 0.1 Pa Pascal (unit) The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre... = 0.1 N/m² Square metre The square metre or square meter is the SI derived unit of area, with symbol m2 . It is defined as the area of a square whose sides measure exactly one metre... = 100 g Gram The gram is a metric system unit of mass.... ·cm⁻¹s Second The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock.... ⁻²
Pounds per square inch Pounds per square inch The pound per square inch or, more accurately, pound-force per square inch is a unit of pressure or of stress based on avoirdupois units...	psi	pressure Pressure Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...	1 psi = 6,894.757 Pa = kPa = 6,894.757 N/m² = Mg·cm⁻¹s⁻²= 6894.757 kg Kilogram The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water... ·cm⁻¹s⁻²
Inch of Mercury Inch of mercury Inches of mercury, ' is a unit of measurement for pressure. It is still widely used for barometric pressure in weather reports, refrigeration and aviation in the United States, but is seldom used elsewhere....	inHg	pressure Pressure Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...	1 inHg = 3386.389 Pa at 0 °C = kPa at 0 °C = 3386.389 N/m² at 0 °C = Mg·cm⁻¹s⁻²= 3386.389 kg·cm⁻¹s⁻²
Millimetre of mercury	mmHg	pressure Pressure Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...	1 mmHg = at 0 °C = at 0 °C = at 0 °C
torr Torr The torr is a non-SI unit of pressure with the ratio of 760 to 1 standard atmosphere, chosen to be roughly equal to the fluid pressure exerted by a millimetre of mercury, i.e., a pressure of 1 torr is approximately equal to 1 mmHg...	Torr	pressure Pressure Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...	1 Torr = Pa = N/m² = kg·cm⁻¹s⁻²

Units officially accepted for use with the SI

Common units not officially sanctioned

See also