Non-SI units accepted for use with SI

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