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,[1][2] 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 |
level of a field quantity |
1 Np = 1[3] |
|
|
level of a power quantity |
1 Np = 1[4] |
bel, decibel |
B, dB |
level of a field quantity |
1 B = ln(10)/2 Np = ln(10)/2[5] |
|
|
level of a power quantity |
1 dB = 0.1 B [6] |
Units with experimentally determined values |
electronvolt |
eV |
energy |
1 eV = 6981160217652999999♠1.60217653(14)×10−19 J |
unified atomic mass unit dalton |
u Da |
mass |
1 u = 1 Da = 6973166053886000000♠1.66053886(28)×10−27 kg |
astronomical unit |
AU[7][8][9] |
length |
1 ua = 7011149597870691000♠1.49597870691(6)×1011 m |
Natural units (n.u.) |
n.u. of speed (speed of light in vacuum) |
c0 |
speed |
7008299792458000000♠299792458 m/s (exact)[10] |
n.u. of action (reduced Planck constant) |
ħ |
action |
6966105457168000000♠1.05457168(18)×10−34 J·s |
n.u. of mass (electron mass) |
me |
mass |
6969910938260000000♠9.1093826(16)×10−31 kg |
n.u. of time |
ħ / mec02 |
time |
6979128808866770000♠1.2880886677(86)×10−21 s |
Atomic units (a.u.) |
a.u. of charge (elementary charge) |
e |
electric charge |
6981160217652999999♠1.60217653(14)×10−19 C |
a.u. of mass (electron mass) |
me |
mass |
6969910938260000000♠9.1093826(16)×10−31 kg |
a.u. of action (reduced Planck constant) |
ħ |
action |
6966105457168000000♠1.05457168(18)×10−34 J·s |
a.u. of length, bohr (Bohr radius) |
a0 |
length |
6989529177210800000♠0.5291772108(18)×10−10 m |
a.u. of energy, hartree (Hartree energy) |
Eh |
energy |
6982435974417000000♠4.35974417(75)×10−18 J |
a.u. of time |
ħ / Eh |
time |
6983241888432650500♠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 = 100 pm |
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 = 7005101325000000000♠101325 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−1·s−2 |
millimetre of mercury |
mmHg |
pressure |
1 mmHg = 7002133322387415000♠133.322387415 Pa at 0 °C = 7002133322387415000♠133.322387415 N/m2 at 0 °C = 7002133322387415000♠133.322387415 kg·cm−1·s−2 at 0 °C |
torr |
Torr |
pressure |
1 Torr = 1/760 atm = 133.322368421... Pa = 133.322368421... N/m2 = 133.322368421... kg·cm−1·s−2 |
See also
References