Non-SI units mentioned in the SI

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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[edit]

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 dimensionless ratio of field quantities LF = ln(F / F0) Np
    dimensionless ratio of power quantities LP = 12 ln(P / P0) Np
bel, decibel B, dB dimensionless ratio of field quantities LF = 2 log10(F / F0) B
    dimensionless ratio of power quantities LP = log10(P / P0) B
Units with experimentally determined values
electronvolt eV energy 1 eV = 1.60217653(14)×10−19 J
unified atomic mass unit
dalton
u
Da
mass 1 u = 1 Da = 1.66053886(28)×10−27 kg
astronomical unit ua[3][4][5] length 1 ua = 1.49597870691(6)×1011 m
Natural units (n.u.)
n.u. of speed (speed of light in vacuum) c0 speed 299792458 m/s (exact)[6]
n.u. of action (reduced Planck constant) ħ action 1.05457168(18)×10−34 J·s
n.u. of mass (electron mass) me mass 9.1093826(16)×10−31 kg
n.u. of time ħ / mec02 time 1.2880886677(86)×10−21 s
Atomic units (a.u.)
a.u. of charge (elementary charge) e electric charge 1.60217653(14)×10−19 C
a.u. of mass (electron mass) me mass 9.1093826(16)×10−31 kg
a.u. of action (reduced Planck constant) ħ action 1.05457168(18)×10−34 J·s
a.u. of length, bohr (Bohr radius) a0 length 0.5291772108(18)×10−10 m
a.u. of energy, hartree (Hartree energy) Eh energy 4.35974417(75)×10−18 J
a.u. of time ħ / Eh time 2.418884326505(16)×10−17 s

Common units not officially sanctioned[edit]

Name Symbol Quantity Equivalent SI unit
ångström, angstrom Å length 1 Å = 0.1 nm = 10−10 m
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 = 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 = 133.322387415 Pa at 0 °C = 133.322387415 N/m2 at 0 °C = 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[edit]

References[edit]

  1. ^ "Non-SI units accepted for use with the SI, and units based on fundamental constants" (PDF). SI brochure (8th edition). BIPM. Retrieved 2010-08-28. 
  2. ^ Taylor, Barry N. (ed.) (2001). "The International System of Units (SI)". Special Publication 330. Gaithersburg, Maryland: National Institute of Standards and Technology (NIST). 
  3. ^ International Bureau of Weights and Measures (2006), The International System of Units (SI) (8th ed.), p. 126, ISBN 92-822-2213-6 
  4. ^ ISO 80000-3
  5. ^ The IAU Style Manual (1989): The Preparation of Astronomical Papers and Reports, p. 23 
  6. ^ In this case it is not the speed of light, but the length of the metre that is obtained by experiment