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SI derived units are units of
measurement ' Measurement is the number, numerical quantification (science), quantification of the 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 meas ...
derived from the seven
base units
base units
specified by the
International System of Units International is an adjective (also used as a noun) meaning "between nations". International may also refer to: Music Albums * International (Kevin Michael album), ''International'' (Kevin Michael album), 2011 * International (New Order album), '' ...
(SI). They are either dimensionless 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 derived unit of frequency in the International System of Units International is an adjective (also used as a noun) meaning "between nations". International may also refer to: Music Albums * International (Kevi ...
, the SI unit of measurement of frequency), but the rest merely reflect their derivation: for example, the
square metre The square metre (American and British English spelling differences#-re, -er, international spelling as used by the International Bureau of Weights and Measures) or square meter (American and British English spelling differences#-re, -er, American ...
(m2), the SI derived unit of area; and the kilogram per cubic metre (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 mass per unit volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter Rho (letter), rho), although the L ...
. 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 derived unit of frequency in the International System of Units International is an adjective (also used as a noun) meaning "between nations". International may also refer to: Music Albums * International (Kevi ...
is "Hz", but the symbol for
metre The metre (British English, Commonwealth spelling) or meter (American English, American spelling; American and British English spelling differences#-re, -er, see spelling differences) (from the French unit , from the Greek noun , "measure", and ...
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 (rad) and the 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 word that indicates, signifies, or is understood as representing an idea, Object (philosophy), object, or wikt:relationship, relationship. Symbols allow people to go beyond what is known or seen ...
, 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 in the International System of Units (SI), the current metric system, having the unit symbol kg. I ...
, bar and electronvolt are not SI units, but are widely used in conjunction with SI units.


Supplementary units

Until 1995, the SI classified the radian and the steradian as ''supplementary units'', but this designation was abandoned and the units were grouped as derived units.


See also

* International System of Quantities (ISQ) * International Vocabulary of Metrology * Metric prefix * Metric system * Planck units


References


Bibliography

*


External links

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