| 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.
- 
