Non-SI units mentioned in the SI

This is a list of units that are not defined as part of the International System of Units (SI), but are otherwise mentioned in the SI, because either the General Conference on Weights and Measures (CGPM) accepts their use as being multiples or submultiples of SI-units, they have important contemporary application worldwide, or are otherwise commonly encountered worldwide.

Units officially accepted for use with the SI

Name	Symbol	Quantity	Equivalent SI unit
Widely used units expected to be used indefinitely
minute	min	time (SI unit multiple)	1 min = 60 s
hour	h	time (SI unit multiple)	1 h = 60 min = 3600 s
day	d	time (SI unit multiple)	1 d = 24 h = 1440 min = 86400 s
degree	°	plane angle (dimensionless unit)	1° = (π / 180) rad
minute	′	plane angle (dimensionless unit)	1′ = (1 / 60)° = (π / 10800) rad
second	″	plane angle (dimensionless unit)	1″ = (1 / 60)′ = (1 / 3600)° = (π / 648000) rad
hectare	ha	area (decimal unit multiple)	1 ha = 100 a = 10000 m2 = 1 hm2
litre	l or L	volume (decimal unit multiple)	1 L = 1 dm3 = 0.001 m3 = 1000 cc = 1000 cm3
tonne	t	mass (decimal unit multiple)	1 t = 103 kg = 1 Mg
Logarithmic units
neper	Np	dimensionless ratio of field quantities	LF = ln(F / F0) Np
		dimensionless ratio of power quantities	LP = 1⁄2 ln(P / P0) Np
bel, decibel	B, dB	dimensionless ratio of field quantities	LF = 2 log10(F / F0) B
		dimensionless ratio of power quantities	LP = log10(P / P0) B
Units with experimentally determined values
electron-volt	eV	energy	1 eV = 1.60217653(14)×10−19 J
atomic mass unit dalton	u Da	mass	1 u = 1 Da = 1.66053886(28)×10−27 kg
astronomical unit	ua	length	1 ua = 1.49597870691(6)×1011 m
Natural units (n.u.)
speed of light	c0	speed	299,792,458 m / s (exact)
reduced Planck constant	ħ	action	1.05457168(18)×10−34 J·s
electron rest mass	me	mass	9.1093826(16)×10−31 kg
n.u. of time	$\hbar/(m_e c_0 ^2)$	time	1.2880886677(86)×10−21 s
Atomic units (a.u.)
elementary charge	e	electric charge	1.60217653(14)×10−19 C
Bohr radius	a0	length	0.5291772108(18)×10−10 m
Hartree energy	Eh	energy	4.35974417(75)×10−18 J
a.u. of time	ħ / Eh	time	2.418884326505(16)×10−17 s

Common units not officially sanctioned

Name	Symbol	Quantity	Equivalent SI unit
Ångström, angstrom	Å	length	1 Å = 0.1 nm = 10−10 m
nautical mile	nm	length	1 nautical mile = 1852 m
knot	kt	speed	1 knot = 1 nautical mile per hour = (1852 / 3600) m / s
are	a	area	1 a = 1 dam2 = 100 m2
barn	b	area	1 b = 10−28 m2
bar	bar	pressure	1 bar = 105 Pa
millibar	mbar	pressure	1 mbar = 1 hPa = 100 Pa
atmosphere	atm	pressure	1 atm = 1013.25 mbar = 1013.25 hPa = 101,325 Pa exactly (commonly used in atmospheric meteorology, in oceanography and for pressures within liquids, or in the industry for pressures within containers of liquefied gas)
dyne per square centimetre (barye)	Ba	pressure	1 Ba = 0.1 Pa = 0.1 N/m2 = 100 g·cm−1s−2
Pounds per square inch	psi	pressure	1 psi = 6,894.757 Pa = 6.894757 kPa = 6,894.757 N/m2 = 6.894757 Mg·cm−1s−2= 6894.757 kg·cm−1s−2
Inch of Mercury	inHg	pressure	1 inHg = 3386.389 Pa at 0 °C = 3.386389 kPa at 0 °C = 3386.389 N/m2 at 0 °C = 3.386389 Mg·cm−1s−2= 3386.389 kg·cm−1s−2
Millimetre of mercury	mmHg	pressure	1 mmHg = 133.322387415 Pa at 0 °C = 133.322387415 N/m2 at 0 °C = 133.322387415 kg·cm−1s−2 at 0 °C
torr	Torr	pressure	1 Torr = 133.322368421... Pa = 133.322368421... N/m2 = 133.322368421... kg·cm−1s−2

See also

• International Vocabulary of Metrology
• International System of Quantities
• International System of Units
• SI base units
• SI prefixes
• SI derived units