Data:CODATA Recommended Values of the Fundamental Physical Constants 1973

Quantity	Symbol	Value	ur
Permeability of vacuum (magnetic constant)	μ0	4π × 10−7 H m−1 ≈ 1.256637061… × 10−6 H m−1	exact
Speed of light in vacuum	c0	2.997 924 58(1.2) × 108 m s−1	4 × 10−9
Permittivity of vacuum (electric constant)	ε0 = (μ0c20)−1	8.854 187 82(7) × 10−12 F m−1	8 × 10−9
Fine structure constant	α = μ0c0e2/2h α−1	0.007 297 3506(60) 137.036 04(11)	8.2 × 10−7 8.2 × 10−7
Elementary charge	e	1.602 1892(46) × 10−19	2.9 × 10−6
Planck constant	h ħ = h/2π	6.626 176 × 10−34 J s 1.054 5887(57) × 10−34 J s	5.4 × 10−6 5.4 × 10−6
Avogadro constant	NA
Atomic mass unit (atomic mass constant)	1 u = (10−3 kg mol−1)/NA mu
Electron rest mass	me
Muon rest mass	mμ
Proton rest mass	mp
Neutron rest mass	mn
Ratio, proton mass to electron mass	mp/me
Ratio, muon mass to electron mass	mμ/me
Specific electron charge	e/me
Faraday constant	F = NAe
Magnetic flux quantum	Φ0 = h/2e h/e
Josephson frequency–voltage ratio (Josephson constant)	e/2h KJ
Quantum of circulation	h/2me h/me
Rydberg constant	R∞
Bohr radius	a0 = α/4πR∞
Electron Compton wavelength	λC(e) = α2/2R∞ λC(e) = λC(e)/2π = αa0

Reference

Cohen, E. Richard; Taylor, B. N. The 1973 Least‐Squares Adjustment of the Fundamental Constants. J. Phys. Chem. Ref. Data 1973, 2 (4), 663–734. DOI: 10.1063/1.3253130.