SI derived unit

SI derived units are units of measurement derived from the seven base units specified by the International System of Units (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 SI unit of measurement of frequency), but the rest merely reflect their derivation: for example, the square metre (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 names of SI derived units, when written in full, are in lowercase. However, the symbols for units named after persons are written with an uppercase initial letter. For example, the symbol for hertz is "Hz"; but the symbol for metre 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).

Named units derived from SI base units

Name	Symbol	Quantity	Equivalents	SI base unit Equivalents
hertz	Hz	frequency	1/s	s−1
radian	rad	angle	m/m	1
steradian	sr	solid angle	m2/m2	1
newton	N	force, weight	kg⋅m/s2	kg⋅m⋅s−2
pascal	Pa	pressure, stress	N/m2	kg⋅m−1⋅s−2
joule	J	energy, work, heat	N⋅m C⋅V W⋅s	kg⋅m2⋅s−2
watt	W	power, radiant flux	J/s V⋅A	kg⋅m2⋅s−3
coulomb	C	electric charge or quantity of electricity	s⋅A F⋅V	s⋅A
volt	V	voltage, electrical potential difference, electromotive force	W/A J/C	kg⋅m2⋅s−3⋅A−1
farad	F	electrical capacitance	C/V s/Ω	kg−1⋅m−2⋅s4⋅A2
ohm	Ω	electrical resistance, impedance, reactance	1/S V/A	kg⋅m2⋅s−3⋅A−2
siemens	S	electrical conductance	1/Ω A/V	kg−1⋅m−2⋅s3⋅A2
weber	Wb	magnetic flux	J/A T⋅m2	kg⋅m2⋅s−2⋅A−1
tesla	T	magnetic field strength, magnetic flux density	V⋅s/m2 Wb/m2 N/(A⋅m)	kg⋅s−2⋅A−1
henry	H	electrical inductance	V⋅s/A Ω⋅s Wb/A	kg⋅m2⋅s−2⋅A−2
degree Celsius	°C	temperature relative to 273.15 K	K	K
lumen	lm	luminous flux	cd⋅sr	cd
lux	lx	illuminance	lm/m2	m−2⋅cd
becquerel	Bq	radioactivity (decays per unit time)	1/s	s−1
gray	Gy	absorbed dose (of ionizing radiation)	J/kg	m2⋅s−2
sievert	Sv	equivalent dose (of ionizing radiation)	J/kg	m2⋅s−2
katal	kat	catalytic activity	mol/s	s−1⋅mol

Other units used with SI

Some other units such as the hour, litre, tonne, 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

Bibliography

• I. Mills, Tomislav Cvitas, Klaus Homann, Nikola Kallay, IUPAC (June 1993). Quantities, Units and Symbols in Physical Chemistry (2nd ed.). Blackwell Science Inc. p. 72.{{cite book}}: CS1 maint: multiple names: authors list (link)