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Measure­ment units

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SI Base Units

NameSym­bolUnit of
secondstime
metermlength
kilogramkgmass
ampereAelectric current
kelvinKthermodynamic temperature
molemolamount of substance
candelacdluminous intensity


SI Derived Units

Name Sym­bol Unit of Equivalent in Base Units Other Equivalents
becquerel Bq activity referred to a radionuclide 1/s
coulomb C electric charge A⋅s V ⋅ F = J ∕ V
degree Celsius °C Celsius temperature K temperature in K − 273.15
farad F capacitance A²⋅s⁴/kg⋅m² C ∕ V = A ⋅ s ∕ V
gray Gy absorbed dose, kerma m²/s² J ∕ kg
henry H inductance kg⋅m²/A²⋅s² Wb ∕ A = V ⋅ s ∕ A
hertz Hz frequency 1/s
joule J energy, work, amount of heat kg⋅m²/s² N ⋅ m = W ⋅ s = Pa ∙ m³
katal kat catalytic activity mol/s
lumen lm luminous flux cd (4 × π) cd ⋅ sr = lx ⋅ m²
lux lx illuminance cd/m² (4 × π) cd ⋅ sr ∕ m² = lm ∕ m²
newton N force kg⋅m/s² J ∕ m = W ⋅ s ∕ m = Pa ⋅ m²
ohm Ω electric resistance kg⋅m²/A²⋅s³ V ∕ A = 1 ∕ S
pascal Pa pressure, stress kg/m⋅s² N ∕ m² = J ∕ m³
radian rad plane angle 1 (0.5 ∕ π) of a circle ≈ 0.159 154 of a circle ≈ 57.296° ≈ 3 437.746′
siemens S electric conductance A²⋅s³/kg⋅m² A ∕ V = 1 ∕ Ω
sievert Sv dose equivalent m²/s² J ∕ kg
steradian sr solid angle 1 (0.25 ∕ π) of a sphere ≈ 0.079 577 of a sphere
tesla T magnetic flux density kg/A⋅s² Wb ∕ m² = N ∕ A ⋅ m
volt V electric potential difference kg⋅m²/A⋅s³ W ∕ A = J ∕ C = Wb ∕ s
watt W power, radiant flux kg⋅m²/s³ J ∕ s = V ⋅ A = N ⋅ m ∕ s
weber Wb magnetic flux kg⋅m²/A⋅s² V ⋅ s = H ⋅ A = T ⋅ m² = J ∕ A




SI Prefixes

Name Sym­bol Number Base 10 Short Scale Long Scale
yotta Y 1 000 000 000 000 000 000 000 000 10²⁴ septillion quadrillion
zetta Z 1 000 000 000 000 000 000 000 10²¹ sextillion trilliard
exa E 1 000 000 000 000 000 000 10¹⁸ quintillion trillion
peta P 1 000 000 000 000 000 10¹⁵ quadrillion billiard
tera T 1 000 000 000 000 10¹² trillion billion
giga G 1 000 000 000 10⁹ billion milliard
mega M 1 000 000 10⁶ million million
kilo k 1 000 10³ thousand thousand
1 10⁰ one one
milli m 0.001 10⁻³ thousandth thousandth
micro μ 0.000 001 10⁻⁶ millionth millionth
nano n 0.000 000 001 10⁻⁹ billionth milliardth
pico p 0.000 000 000 001 10⁻¹² trillionth billionth
femto f 0.000 000 000 000 001 10⁻¹⁵ quadrillionth billiardth
atto a 0.000 000 000 000 000 001 10⁻¹⁸ quintillionth trillionth
zepto z 0.000 000 000 000 000 000 001 10⁻²¹ sextillionth trilliardth
yocto y 0.000 000 000 000 000 000 000 001 10⁻²⁴ septillionth quadrillionth
SI prefixes which are not multiples or sub-multiples of 1 000
hecto h 100 10² hundred hundred
deca da 10 10¹ ten ten
1 10⁰ one one
deci d 0.1 10⁻¹ tenth tenth
centi c 0.01 10⁻² hundredth hundredth


Prefixes for powers of 2

Name Sym­bol Number Base 2 Short Scale Long Scale
yobi Yi 1 208 925 819 614 629 174 706 176 2⁸⁰ ≈ 1.2 septillion ≈ 1.2 quadrillion
zebi Zi 1 180 591 620 717 411 303 424 2⁷⁰ ≈ 1.2 sextillion ≈ 1.2 trilliard
exbi Ei 1 152 921 504 606 846 976 2⁶⁰ ≈ 1.2 quintillion ≈ 1.2 trillion
pebi Pi 1 125 899 906 842 624 2⁵⁰ ≈ 1.1 quadrillion ≈ 1.1 billiard
tebi Ti 1 099 511 627 776 2⁴⁰ ≈ 1.1 trillion ≈ 1.1 billion
gibi Gi 1 073 741 824 2³⁰ ≈ 1.1 billion ≈ 1.1 milliard
mebi Mi 1 048 576 2²⁰ ≈ 1.0 million ≈ 1.0 million
kibi Ki 1 024 2¹⁰ ≈ 1.0 thousand ≈ 1.0 thousand
1 2⁰ one one




Non-SI units accepted for use with the SI

Name Sym­bol Unit of Equivalent in SI Units Other Equivalents
minute min time 60 s 1 ∕ 1 440 d = 1 ∕ 60 h
hour h time 3 600 s 1 ∕ 24 d = 60 min
day d time 86 400 s 24 h = 1 440 min
degree of arc ° plane angle, phase angle (π ∕ 180) rad 60′ = 3 600″ = 1 ∕ 360 of a circle ≈ 0.017 453 293 rad
minute of arc plane angle, phase angle (π ∕ 10 800) rad 1 ∕ 60° = 60″ = 1 ∕ 21 600 of a circle ≈ 290.888 209 μrad
second of arc plane angle, phase angle (π ∕ 648 000) rad 1 ∕ 3 600° = 1 ∕ 60′ = 1 ∕ 1 296 000 of a circle ≈ 4.848 137 μrad
liter l, L volume 0.001 m³ 1 000 000 mm³ = 1 000 cm³ = 10 cm × 10 cm × 10 cm
tonne t mass 1 000 kg 1 Mg = 1 000 000 g
hectare ha area 10 000 m² 0.01 km² = 100 m × 100 m
bel B logarithmic ratio quantities 1 0.5 × (ln 10) Np ≈ 1.151 292 Np
neper Np logarithmic ratio quantities 1 2 ∕ (ln 10) B ≈ 0.868 588 B
electronvolt eV energy 160.217 663 4 × 10⁻²¹ J ≈ 160.218 zJ
dalton Da mass ≈ 1.660 539 04 × 10⁻²⁷ kg ≈ 1.660 539 yg
astronomical unit au length 149.597 870 7 × 10⁻⁹ m 149.597 870 7 Gm

The dalton used to be called unified atomic mass unit [u]. The astronomical unit used to have the symbol ua.
The gal [Gal] is an unit of acceleration, equalling 0.01 m/s, 1 cm/s or 0.036 km/h.




Other important units

NameSym­bolUnit ofEquivalent
yearatime≈ 365.25 d
monthtime≈ 30.44 d
weektime7 d
bitbitdigital information
byteBdigital information8 bit



Additional units permitted in the European Union 🇪🇺

NameSym­bolUnit ofEquivalent
barbarpressure, stress100 000 Pa = 100 kPa
revolutionplane angle(2 × π) rad = 360° = 1 ∕ 1 of a circle ≈ 6.283 185 rad
grade, gon gonplane angle(π ∕ 200) rad = 0.9° = 1 ∕ 400 of a circle ≈ 0.015 708 rad
dioptrevergency of optical systems1 ∕ m
metric caratmass of precious stones0.000 2 kg = 0.2 g = 200 mg
areaarea of farmland and building land100 m² = 0.01 ha = 10 m × 10 m
textexmass per unit length of textile yarns and threads0.000 001 kg ∕ m = 1 μg ∕ m = 1 g ∕ km
millimetre of mercurymm Hgblood pressure and pressure of other body fluids133.322 Pa
barnbeffective cross-sectional area1 × 10⁻²⁸ m² = 100 fm²

Source: European Directive 80/181/EEC, as amended on 2019-07-23.





Unicode symbols

Symbol Code point Name
Symbols for measurement units and prefixes
° 00B0 Degree sign
Ω 03A9 Greek capital letter omega
2032 Prime
2033 Double prime
μ 03BC Greek small letter mu
Decimal separators and spaces
, 002C Comma
. 002E Full stop
2020 Space
20A0 No-break space
202F Narrow no-break space
Mathematical symbols
+ 002B Plus sign
2212 Minus sign
22C5 Dot operator
× 00D7 Multiplication sign
÷ 00F7 Division sign
2215 Division slash
/ 002F Solidus
± 00B1 Plus-minus sign
= 003D Equals sign
2248 Almost equal to
% 0025 Percent sign
2030 Per mille sign
π 03C0 Greek small letter pi
Superscript numbers and mathematical symbols
207A Superscript plus sign
207B Superscript minus
2070 Superscript zero
¹ 00B9 Superscript one
² 00B2 Superscript two
³ 00B3 Superscript three
2074 Superscript four
2075 Superscript five
2076 Superscript six
2077 Superscript seven
2078 Superscript eight
2079 Superscript nine




Obsolete units which used to be permitted fully or partly in the European Union 🇪🇺

NameSym­bolUnit ofEquivalent
curieCiactivity (of a radionuclide)37 000 000 000 Bq = 37 GBq
radradabsorbed dose0.01 Gy = 10 mGy
remremequivalent dose0.01 Sv = 10 mSv
röntgenRexposure (X and γ rays)0.000 258 C ∕ kg = 258 μC ∕ kg
poisePdynamic viscosity0.1 Pa ⋅ s = 0.1 N ⋅ s ∕ m²
stokesStkinematic viscosity0.000 1 m² ∕ s
dynedynforce0.000 01 N = 10 μN
ergergenergy0.000 000 1 J = 100 nJ
galGalacceleration due to gravity0.01 m ∕ s²
ångströmÅwavelength, atomic distances0.000 000 000 1 m = 100 pm
quintalqmass100 kg
standard atmosphereatmpressure101 325 Pa = 101.325 kPa
FestmeterFmvolume (forestry and timber trade)1 m³
Raummeter, stèreRm, stvolume (forestry and timber trade)1 m³
kilogramme-force, kilopondkgf, kpforce9.806 65 N
torrpressure(101 325 ∕ 760) Pa ≈ 133.322 368 Pa
technical atmosphereatpressure98 066.5 Pa = 98.066 5 kPa
metre of watermH₂0pressure9 806.65 Pa = 9.806 65 kPa
Pferdestärke, Paardekracht, cheval vapeur, cavallo vaporePS, pk, CV, cvpower735.498 75 W
caloriecalquantity of heat4.186 8 J
thermiethquantity of heat4 186 800 J = 4.186 8 MJ
frigoriefgquantity of heat4 186.8 J = 4.186 8 kJ
stilbsbluminance10 000 cd ∕ m²
inchinlength≈ 0.025 4 m ≈ 2.54 cm
footftlength≈ 0.304 8 m ≈ 30.48 cm
milelength≈ 1 609 m ≈ 1.609 km
yardydlength≈ 0.914 4 m ≈ 91.44 cm
square footsq ftarea≈ 0.092 9 m² ≈ 929 cm²
acreacarea≈ 4 047 m² ≈ 0.404 7 ha
square yardsq ydarea≈ 0.836 1 m² ≈ 8 361 cm²
fluid ouncefl ozvolume≈ 0.000 028 41 m³ ≈ 0.028 41 l ≈ 28.41 ml
gillvolume≈ 0.000 142 1 m³ ≈ 0.142 1 l ≈ 142.1 ml
pintptvolume≈ 0.000 568 3 m³ ≈ 0.568 3 l ≈ 568.3 ml
quartqtvolume≈ 0.001 137 m³ ≈ 1.137 l
gallongalvolume≈ 0.004 546 m³ ≈ 4.546 l
ounce (avoirdupois)ozmass≈ 0.028 35 kg ≈ 28.35 g
troy ounceoz trmass≈ 0.031 1 kg ≈ 31.1 g
poundlbmass≈ 0.453 6 kg ≈ 453.6 g
thermenergy≈ 105 506 000 J ≈ 105.506 MJ ≈ 29.307 2 kWh
fathomfmlength≈ 1.829 m

The grade or gon also used to have the unit symbol ᵍ. The kelvin also used to be called degree kelvin and had the unit symbol °K.

Source: European Directives 71/354/EEC (1971) and 80/181/EEC.