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# 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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