Non-SI units accepted for use with SI

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The following units are not SI units but are "accepted for use with the International System."^[1]

Non-SI units accepted for use with SI

Name	Symbol	Quantity	Equivalent SI unit
minute	min	time (multiple unit)	1 min = 60 s
hour	h	time (multiple unit)	1 h = 60 min = 3600 s
day	d	time (multiple unit)	1 d = 24 h = 1440 min = 86400 s
degree of arc	°	angle (non unitary unit)	1° = (π/180) rad
minute of arc	′	angle (non unitary unit)	1′ = (1/60)° = (π/10800) rad
second of arc	″	angle (non unitary unit)	1″ = (1/60)′ = (1/3600)° = (π/648000) rad
hectare	ha	area (simple decimal multiple unit)	1 ha = 100 a = 10000 m²
litre	l or L	volume (simple decimal multiple unit)	1 dm3 = 0.001 m3
tonne	t	mass (simple decimal multiple unit)	1 t = 103 kg = 1 Mg

Non-SI units not formally adopted by the CGPM

Name	Symbol	Quantity	Equivalent SI unit
neper, field quantity	Np	ratio (dimensionless)	LF = ln(F/F0) Np
neper, power quantity	Np	ratio (dimensionless)	LP = 1⁄2ln(P/P0) Np
bel, field quantity	B	ratio (dimensionless)	LF = 2 log10(F/F0) B
bel, power quantity	B	ratio (dimensionless)	LP = log10(P/P0) B

Non-SI units with values obtained only by experiment^[1]

Name	Symbol	Quantity	Equivalent SI unit
electronvolt	eV	energy	1 eV = 1.60217653(14)×10−19 J
atomic mass unit	u	mass	1 u = 1.66053886(28)×10−27 kg
astronomical unit	AU	length	1 AU = 1.49597870691(6)×1011 m

Non-SI units whose use is not encouraged

Name	Symbol	Quantity	Equivalent SI unit
Ångström, angstrom	Å	length	1 Å = 0.1 nm = 10−10 m
nautical mile		length	1 nautical mile = 1852 m
knot		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 (was used in atmospheric meteorology, the preferred unit is now the hectopascal)
atmosphere	atm	pressure	1 atm = 1013.25 mbar = 1013.25 hPa = 1.01325×105 Pa (commonly used in atmospheric meteorology, in oceanology and for pressures within liquids, or in the industry for pressures within containers of liquified gas)

[edit] References

1. ^ ^{a b} "Non-SI units accepted for use with the SI, and units based on fundamental constants". SI brochure (8th edition). BIPM. http://www.bipm.org/en/si/si_brochure/chapter4/4-1.html. Retrieved on 24 March 2009. 

• Taylor, Barry N. (ed.) (2001). The International System of Units (SI) (2001 ed., Special Publication 330). Gaithersburg, Maryland: National Institute of Standards and Technology. pp. 15–19. Viewed at http://physics.nist.gov/Pubs/SP330/sp330.pdf
• "Non-SI units accepted for use with the SI, and units based on fundamental constants". SI brochure (8th edition). BIPM. http://www.bipm.org/en/si/si_brochure/chapter4/4-1.html. Retrieved on 24 March 2009.