Measure­ment units

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SI Base Units

Name Symbol Unit of
second s time
meter m length
kilogram kg mass
ampere A electric current
kelvin K thermodynamic temperature
mole mol amount of substance
candela cd luminous 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

Name Symbol Unit of Equivalent
year a time ≈365 d
month time ≈30 d
week time 7 d
bit bit digital information
Byte B digital information 8 bit




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