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Definition

Table of Physical Constants

Physical Constants
Quantity or phenomenon Symbol SI unit value Alternate unit value
astronomical unit AU 1.4959787 x 1011
meters
1.4959787 x 108
kilometers
atomic mass unit amu 1.67377 x 10-27
kilogram
1.67377 x 10-24
gram
Avogadro constant N, L 6.022169 x 1023 6.022169 x 1023
Bohr magneton µB 9.274 x 10-24
joule per tesla
9.274 x 10-28
joule per gauss
Bohr radius ao 5.29177 x 10-11
meter
5.29177 x 10-9
centimeter
Boltzmann's constant k 1.3807 x 10-23
joule per kelvin
1.3807 x 10-16
erg per kelvin
characteristic impedance
of free space
Zo 377
ohms
--
Compton wavelength of electron ce 2.4263 x 10-12
meter
2.4263 x 10-10
centimeter
Compton wavelength of proton cp 1.3214 x 10-15
meter
1.3214 x 10-13
centimeter
Compton wavelength of neutron cn 1.3196 x 10-15
meter
1.3196 x 10-13
centimeter
Earth's mass mearth 5.974 x 1024
kilograms
5.974 x 1027
grams
Earth's mean orbital speed vearth 30
kilometers per second
18.5
miles per second
Earth's mean radius rearth 6.371 x 106
meters
6371
kilometers
electron radius re 2.81794 x 10-15
meter
2.81794 x 10-13
centimeter
electron rest mass me 9.10956 x 10-31
kilogram
9.10956 x 10-28
gram
elementary charge e 1.60 x 10-19
coulomb
--
Euler's constant 0.577216 0.577216
Faraday constant F 9.65 x 104
coulombs per mole
--
fine structure constant 0.007297 0.007297
first radiation constant c1 4.9926 x 10-24
joule-meter
4.9926 x 10-15
erg-centimeter
gas constant R 8.3145
joules per kelvin per mole
8.3145 x 107
ergs per kelvin per mole
gravitational acceleration
at Earth's surface
g 9.8067
meters per second squared
980.67
centimeters per second squared
gravitational constant G 6.67 x 10-11
newton meter squared
per kilogram squared
--
Hartree energy Eh 4.3597 x 10-18
joule
4.3597 x 10-11
erg
Moon's mass mmoon 7.348 x 1022
kilograms
7.348 x 1025
grams
Moon's mean radius rmoon 1.738 x 106
meters
1738
kilometers
natural logarithm base e 2.718282 2.718282
neutron radius rn * *
neutron rest mass mn 1.67492 x 10-27
kilogram
1.67492 x 10-24
gram
nuclear magneton µn 5.051 x 10-27
joule per tesla
5.051 x 10-31
joule per gauss
permeability of free space µo 1.257 x 10-6
henry per meter
1.257
microhenrys per meter
permittivity of free space o 8.85 x 10-12
farad per meter
8.85
picofarads per meter
pi 3.14159 3.14159
Planck's constant h 6.626176 x 10-34
joule-second
6.626176 x 10-27
erg-second
proton radius rp 2 x 10-16
meter *
2 x 10-14
centimeter *
proton rest mass mp 1.67261 x 10-27
kilogram
1.67261 x 10-24
gram
Rydberg constant R or RH 1.097 x 107
per meter
1.097 x 105
per centimeter
second radiation constant c2 0.014388
meter-kelvin
1.4388
centimeter-kelvin
speed of light c 2.99792 x 108
meters per second
2.99792 x 1010
centimeters per second
speed of sound in air vsound 331.4
meters per second
1087
feet per second
Stefan-Boltzmann constant 5.67 x 10-8
watt per meter squared
per kelvin to the fourth
--
Sun's mass msun 1.989 x 1030
kilograms
1.989 x 1033
grams
Sun's mean radius rsun 6.970 x 108
meters
6.970 x 105
kilometers
Wien's constant w 2.898 x 10-3
meter-kelvin
0.2898
centimeter-kelvin

All values are approximations, accurate to the number of significant digits shown.

*Value depends on environment.

This was last updated in September 2005
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