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SI derived units are units of
measurement Measurement is the quantification (science), quantification of variable and attribute (research), attributes of an object or event, which can be used to compare with other objects or events. The scope and application of measurement are dependen ...

measurement
derived from the seven
base units
base units
specified by the
International System of Units The International System of Units, known by the international abbreviation SI in all languages and sometimes Pleonasm#Acronyms_and_initialisms, pleonastically as the SI system, is the modern form of the metric system and the world's most wi ...
(SI). They are either
dimensionless In dimensional analysis In engineering and science, dimensional analysis is the analysis of the relationships between different physical quantities by identifying their base quantity, base quantities (such as length, mass, time, and electric curre ...
or can be expressed as a product of one or more of the base units, possibly scaled by an appropriate power of exponentiation. The SI has special names for 22 of these derived units (for example,
hertz The hertz (symbol: Hz) is the unit Unit may refer to: Arts and entertainment * UNIT Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action ...

hertz
, the SI unit of measurement of frequency), but the rest merely reflect their derivation: for example, the
square metre The square metre ( international spelling as used by the International Bureau of Weights and Measures The International Bureau of Weights and Measures (french: Bureau international des poids et mesures, BIPM) is an intergovernmental organi ...
(m2), the SI derived unit of area; and the
kilogram per cubic metre The kilogram per cubic metre (symbol: kg·m−3, or kg/m3) is an SI derived unit of density, defined by mass in kilograms divided by volume in cubic metres. Conversions 1 kg/m3 is equivalent to: : = 0.001 gram per cubic centimetre, g/cm3 (ex ...
(kg/m3 or kg⋅m−3), the SI derived unit of
density The density (more precisely, the volumetric mass density; also known as specific mass), of a substance is its per unit . The symbol most often used for density is ''ρ'' (the lower case Greek letter ), although the Latin letter ''D'' can also ...

density
. The names of SI derived units, when written in full, are always in lowercase. However, the symbols for units named after persons are written with an uppercase initial letter. For example, the symbol for
hertz The hertz (symbol: Hz) is the unit Unit may refer to: Arts and entertainment * UNIT Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action ...

hertz
is "Hz", but the symbol for
metre The metre ( Commonwealth spelling) or meter (American spelling Despite the various English dialects spoken from country to country and within different regions of the same country, there are only slight regional variations in English ...
is "m".


Derived units with special names

The International System of Units assigns special names to 22 derived units, which includes two dimensionless derived units, the
radian The radian, denoted by the symbol \text, is the SI unit The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric sy ...

radian
(rad) and the
steradian The steradian (symbol: sr) or square radian is the SI unit of solid angle. It is used in three-dimension thumb , 236px , The first four spatial dimensions, represented in a two-dimensional picture. In physics Physics (from gr ...

steradian
(sr).


Examples of derived quantities and units


Other units used with SI

Some other units such as the
hour An hour (symbol A symbol is a mark, sign, or that indicates, signifies, or is understood as representing an , , or . Symbols allow people to go beyond what is n or seen by creating linkages between otherwise very different s and s. All ...
,
litre The litre (British English British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial codification of grammar and ...

litre
,
tonne The tonne ( or ; symbol: t) is a metric unit of mass equal to 1,000 kilogram The kilogram (also kilogramme) is the base unit of mass Mass is the physical quantity, quantity of ''matter'' in a physical body. It is also a meas ...
,
bar Bar or BAR may refer to: Food *Bar (establishment) A bar is a long raised narrow table or bench designed for dispensing beer or other alcoholic beverage, alcoholic drinks. They were originally chest high, and a bar, often brass, ran the len ...
, and
electronvolt In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular suc ...
are not SI units, but are widely used in conjunction with SI units.


Supplementary units

Until 1995, the SI classified the
radian The radian, denoted by the symbol \text, is the SI unit The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric sy ...

radian
and the
steradian The steradian (symbol: sr) or square radian is the SI unit of solid angle. It is used in three-dimension thumb , 236px , The first four spatial dimensions, represented in a two-dimensional picture. In physics Physics (from gr ...

steradian
as ''supplementary units'', but this designation was abandoned and the units were grouped as derived units.


See also

*
International System of Quantities The International System of Quantities (ISQ) consists of the quantities Quantity is a property that can exist as a Counting, multitude or Magnitude (mathematics), magnitude, which illustrate discontinuity (mathematics), discontinuity and continu ...
(ISQ) * International Vocabulary of Metrology *
Metric prefix A metric prefix is a unit prefix that precedes a basic unit of measure to indicate a multiple (mathematics), multiple or submultiple of the unit. All metric prefixes used today are decimal, decadic. Each prefix has a unique symbol that is prepende ...
*
Metric system The metric system is a system of measurement A system of measurement is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purpose ...

Metric system


References


Bibliography

*


External links

* {{Portal bar, Physics Derived sv:SI-enhet#Härledda enheter