Definition:SI Units/Base Units

Definition

The base SI units are as follows:

SI Base Units

Name	Unit symbol	Dimension	Symbol
metre	$\mathrm m$	$\mathsf L$: Length	$l$
kilogram	$\mathrm {kg}$	$\mathsf M$: Mass	$m$
second	$\mathrm s$	$\mathsf T$: Time	$t$
ampere	$\mathrm A$	$\mathsf I$: Electric Current	$I$
kelvin	$\mathrm K$	$\Theta$: Temperature	$T$
candela	$\mathrm {cd}$	$\mathsf J$: Luminous Intensity	$I_v$
mole	$\mathrm {mol}$	$\mathsf N$: Amount of Substance	$n$

SI Supplementary Units

The supplementary SI units are as follows:

SI Supplementary Units

Name	Unit symbol	Dimension	Used for	Symbol
radian	$\mathrm {rad}$	$\text {none}$	plane angle	$\theta$
steradian	$\mathrm {sr}$	$\text {none}$	solid angle

Also defined as

Some sources categorize the supplementary units as base units.

Some, however, categorize them as derived SI units.

The decision to treat them as separate from both, and to use them directly for the construction of further derived SI units, has been generally accepted.

Also see

• Definition:Metric Scaling Prefixes

Sources

• 1964: Milton Abramowitz and Irene A. Stegun: Handbook of Mathematical Functions ... (previous) ... (next): $2$. Physical Constants and Conversion Factors
• 1969: J.C. Anderson, D.M. Hum, B.G. Neal and J.H. Whitelaw: Data and Formulae for Engineering Students (2nd ed.) ... (previous) ... (next): $1.$ Units and Abbreviations: $1.2$ SI units $(1)$ Basic units
• 1976: Ralph J. Smith: Circuits, Devices and Systems (3rd ed.) ... (previous) ... (next): Chapter $1$: Electrical Quantities: Definitions and Laws: The International System of Units: Table $1$-$1$ Basic Quantities
• 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): SI units
• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): SI units