There are certain nonSI units that are accepted for use with the SI. These include units which are in continuous everyday use, in particular the traditional units of time and of angle, together with a few other units which have assumed increasing technical importance and those needed for commercial, legal and specialist scientific interests or for the interpretation of older texts.
NonSI units accepted for use with the International System
Quantity 
Name of unit 
Symbol for unit 
Value in SI units 
time

minute
hour
day

min
h
d

1 min = 60 s
1 h = 60 min = 3,600 s
1 d = 24 h = 86,400 s

length

astronomical unit ^{(a)}

au

1 au = 149,597,870,700 m

plane and phase angle

degree
minute
second ^{(b)}

º
'
''

1º = (π/180) rad
1' = (1/60)º = (π/10,800) rad
1" = (1/60)' = (π/648,000) rad

area

hectare ^{(c)}

ha

1 ha = 1 hm^{2} = 10^{4} m^{2}

volume

litre ^{(d)}

l, L

1 l = 1 L = 1 dm^{3} = 10^{3} cm^{3} = 10^{3} m^{3}

mass

tonne ^{(e)}
dalton ^{(f)}

t
Da

1 t = 10^{3 }kg
1 Da = 1.660,539,066,60 (50) x 10^{27 }kg

energy

electronvolt ^{(g)}

eV

1 eV = 1.602,176,634 x 10^{19} J

logarithmic ratio quantities

neper ^{(h)}
bel ^{(h)}
decibel ^{(h)}

Np
B
dB

see text

(a) As decided at the XXVIII General Assembly of the International Astronomical Union.
(b) For some applications such as in astronomy, small angles are measured in arcseconds (i.e. seconds of plane angle), denoted as or ″, or milliarcseconds, microarcseconds and picoarcseconds, denoted mas, μas and pas, respectively, where arcsecond is an alternative name for second of plane angle.
(c) The unit hectare and its symbol, ha, were adopted by the CIPM in 1879. The hectare is used to express land area.
(d) The litre and the symbol, lowercase l, were adopted by the CIPM in 1879. The alternative symbol, capital L, was adopted by the 16th CGPM in order to avoid the risk of confusion between the letter l (el) and the numeral 1 (one).
(e) The tonne and its symbol, t, were adopted by the CIPM in 1879. This unit is sometimes referred to as “metric ton” in some Englishspeaking countries.
(f) The dalton (Da) and the unified atomic mass unit (u) are alternative names (and symbols) for the same unit, equal to 1/12 of the mass of a free carbon 12 atom, at rest and in its ground state. This value of the dalton is the value recommended in the CODATA 2018 adjustment.
(g) The electronvolt is the kinetic energy acquired by an electron in passing through a potential difference of one volt in vacuum. The electronvolt is often combined with the SI prefixes.
(h) In using these units it is important that the nature of the quantity be specified and that any reference value used be specified.
This table, which is an extract of the 9^{th} edition of The International System of Units brochure published by BIPM, also includes the units of logarithmic ratio quantities, the neper, bel and decibel. The notes in the SI brochure provide more information on their use.
You can read more about the SI units and nonSI units in the full SI brochure.