Non-SI units accepted for use with SI

SI coherent units have the advantage that unit conversions are not required when inserting particular values for quantities into quantity equations.

Nonetheless it is recognised that some non-SI units are widely used and are expected to continue to be used for many years. Therefore, some non-SI units are accepted for use with the SI. If these units are used, some advantages of the SI are lost.

The SI prefixes can be used with several of these units, but not, for example, with the non-SI units of time.

Name	Symbol	Quantity	Value in SI units
tonne	t	mass	1 Mg 103 kg
dalton	Da	mass	1.660 539 040 (20) × 10−27 kg 1.660 539 040 (20) yg
astronomical unit	au	length	149 597 870 700 m 149.597 870 7 Gm
hectare	ha	area	1 hm2 104 m2
litre	L, l	volume	1 dm3 103 cm3 10−3  m3
minute	min	time	60 s
hour	h	time	3600 s
day	d	time	86 400 s
electronvolt	eV	energy	1.602 176 634 × 10−19 J
degree	°	plane angle	(π / 180) rad
minute	′	plane angle	(π / 10 800) rad
second	″	plane angle	(π / 648 000) rad

Non-SI logarithmic units accepted for use with SI

Name	Symbol	Quantity	Value in SI units
neper	Np	logarithmic ratio
bel	B	logarithmic ratio
decibel	dB	logarithmic ratio