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Recommended Values of Physical Constants and Conversion Factors

Please read the notes following the table.

speed of light in a vacuum (c)2.99792458E+08 m/s (exact)
permeability of a vacuum (µ0)4π×1.0E-07 H/m
permittivity of a vacuum (ε0)8.854187817...E-12 F/m
elementary charge (of proton)1.60217733(49)E-19 C
gravitational constant6.67259(85)E-11 Nm2kg-2
unified atomic mass constant (mu = mass 12C / 12)1.6605402(10)E-27 kg
rest mass of electron (me) 9.1093897(54)E-31 kg
5.48579903(13)E-04 amu
rest mass of proton (mp)1.6726231(10)E-27 kg
1.007276470(12) amu
1836.152701(37) me
rest mass of neutron (mn)1.6749286(10)E-27 kg
1.008664904(14) amu
energy equivalence of rest mass of electron0.5109906(15) MeV
energy equivalence of rest mass of proton938.27231(28) MeV
energy equivalence of rest mass of neutron939.56563(28) MeV
electron specific charge (-e/me)-1.75881962(53)E11 C/kg
Planck constant6.6260755(40)E-34 Js
h/2π1.05457266(63)E-34 Js
Rydberg constant1.0973731534E+07 1/m
fine structure constant7.29735308(33)E-03
reciprocal fine structure constant137.0359895(61)
Hartree energy4.3597482(26)E-18 J
2.6255000E+06 J/mol
27.211652 eV
627.51E+03 Calories/mol (US Calorie)
Bohr radius5.29177249(24)E-11 m
electron radius2.81794092(38)E-15 m
Compton wavelength of electron2.42631058(22)E-12 m
Compton wavelength of proton1.32141002(12)E-15 m
Compton wavelength of neutron1.31959110(12)E-15 m
Avogadro constant (NA, L)6.0221367(36)E+23 1/mol
Faraday constant9.6485309(29)E+04 C/mol
molar gas constant8.314510(70) J/K/mol
Boltzman constant1.380658(12)E-23 J/K
Stefan-Boltzman constant5.67051(19)E-08 W/m2K-4
first radiation constant3.7417749(22)E-16 Jm2s-1
second radiation constant1.438769(12)E-02 mK
Bohr magneton9.2740154(31)E-24 J/T
nuclear magneton5.0507866(17)E-27 J/T
magnetic flux quantum2.06783461(61)E-15 Vs
gyromagnetic ratio of proton2.67522128(81)E+08 1/s/T
*1/2π4.2577469(13)E+07 Hz/T
in pure water2.67515255(81)E+08 1/s/T
*1/2π4.2756375(13)E+07 Hz/T
magnetic moment of electron9.2847701(31)E-24 J/T
in terms of Bohr magneton1.001159652(10)
magnetic moment of proton1.41060761(47)E-26 J/T
in terms of Bohr magneton1.521032202(15)E+03
in pure water1.520993129(17)E+03
in terms of nuclear magneton2.792847386(63)
Electronvolts per mol96.485333E+03 J/mol
23.060548E+03 Calories/mol
1/cm (harmonic oscillator)9.93223731E-24 J
5.98132908 J/mol
8.06554093 E-3 eV
Calorie (USA - definition)4.18400 J
Mean Calorie4.19002 J
15 deg C Calorie4.1890 J
220 lattice parameter of silicon (d220 = a/80.5)1.92015540(40)E-13


The above values are taken from Refs. [1-3]: these are good enough for most purposes.  Recently new values have been published which are considerably more accurate, except for the gravitational constant, G.  For details of these please see Ref. [4] and the NIST website.


  1. E. R. Cohen and B. N. Taylor, "The 1986 CODATA recommended values of the fundamental physical constants.", J. Res. National Bureau of Standards, 92(2), 85-95 (1987).
  2. E. R. Cohen and B. N. Taylor, "The 1986 adjustment of the fundamental physical constants", CODATA Bulletin Number 63, (1986); and Rev. Mod. Phys., 59(4), 1121-1148 (1987).
  3. CRC Handbook of Chemistry and Physics, 58th edition (1977-78).
  4. P. J. Mohr and B. N. Taylor, "CODATA recommended values of the fundamental physical constants: 1998", J. Phys. Chem. Ref. Data, 28(6) (1999); and Rev. Mod. Phys., 72(2), 1713-1852, (2000).

The number in parenthesis after each value is the estimated standard deviation uncertainty of the last digit quoted.

Other Sources of Information:

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Last modified: Tue Nov 18 16:00:08 GMT 2003 Chris Latham, Chris Ewels.

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