| 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
Posted by: Margaret Rouse
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