SI derived unit

The International System of Units (SI) specifies a set of seven base units from which all other SI units of measurement are derived. Each of these other units (SI derived units) is either dimensionless or can be expressed as a product of (positive or negative, but usually integral) powers of one or more of the base units.

For example, the SI derived unit of area is the square metre (m²), and the SI derived unit of density is the kilogram per cubic metre (kg/m³ or kg m⁻³). The degree Celsius (see the table below) has a somewhat unclear status, and is arguably an exception to this rule. The names of SI units are written in lowercase. The symbols for units named after persons, however, are always written with an uppercase initial letter (e.g. the symbol for the hertz is "Hz"; but the symbol for the metre is "m").

Derived units with special names

In addition to the two dimensionless derived units radian (rad) and steradian (sr), 20 other derived units have special names.

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	dimensionless
steradian	sr	solid angle	m2/m2	dimensionless
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	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	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	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, and electron volt 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 System of Units (SI)
• International Vocabulary of Metrology
• Metric prefix
• Metric system
• Non-SI units mentioned in the SI
• Planck units
• SI base unit

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)