| 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.