The values are derived from the consistent set of constants which were produced by E.R. Cohen & B.N. Taylor (CODATA Bull. no. 63 (1986)) in collaboration with the CODATA Task Group on Fundamental Physical Constants and were subsequently recommended for general adoption by CODATA. This reference must be included when these constants are used in a context where their full accuracy is important. The number in parenthesis after each value is the estimated standard-deviation uncertainty of the last digit quoted.

Quantity	Symbol	Value (with s.d. uncertainty)
speed of light in vacuum	c	2.99792458 x 108 m.s-1 (exact)
permeability of a vacuum	m0	4p x 10-7 H.m-1
permittivity of a vacuum, 1/m0c2	e0	8.854187817... x 10-12 F.m-1
elementary charge (of proton)	e	1.60217733(49) x 10-19 C
gravitational constant	G	6.67259(85) x 10-11 N.m2.kg-2
unified atomic mass constant	mu	1.6605402(10) x 10-27 kg
rest mass:
- of electron	me	9.1093897(54) x 10-31 kg
	me/mu	5.48579903(13) x 10-4
- of proton	mp	1.6726231(10) x 10-27 kg
	mp/mu	1.007276 470(12)
	mp/me	1836.152701(37)
- of neutron	mn	1.6749286(10) x 10-27 kg
	mn/mu	1.008664904(14)
energy equivalence of rest mass:
- of electron, mec2/(e/C)		0.51099906(15) MeV
- of proton, mpc2/(e/C)		938.27231(28) MeV
- of neutron, mnc2/(e/C)		939.56563(28) MeV
Planck constant	h	6.6260755(40) x 10-34 J.s
h/2p	h	1.054572 66(63) x 10-34 J.s
Rydberg constant, m02mee4c3/8h3	R?	1.0973731534(13) x 107 m-1
fine structure constant, m0e2c/2h	a	7.29735308(33) x 10-3
(m0e2c/2h)-1	a-1	137.0359895(61)
Hartree energy, 2R?hc	Eh	4.3597482(26) x 10-18 J
Bohr radius, h2(pm0c2mee2)	a0	5.291772 49(24) x 10-11 m
electron radius, m0e2/(4pme)	re	2.81794092(38) x 10-15 m
Compton wavelength:
- of electron, h/mec	lC	2.42631058(22) x 10-12 m
- of proton, h/mpc	lC,p	1.32141002(12) x 10-15 m
- of neutron, h/mnc	lC,n	1.31959110(12) x 10-15 m
Avogadro constant	L, NA	6.0221367(36) x 1023 mol-1
Faraday constant	F	9.6485309(29) x 104 C.mol-1
molar gas constant	R	8.314510(70) J.K-1.mol-1
Boltzmann constant, R/L	k	1.380658(12) x 10-23 J.K-1
Stefan-Boltzmann constant	s	5.67051(19) x 10-8 W.m-2.K-4
first radiation constant, 2phc2	c1	3.7417749(22) x 10-16 J.m2.s-1
second radiation constant, hc/k	c2	1.438769(12) x 10-2 m.K
Bohr magneton, eh/2me	mB	9.2740154(31) x 10-24 J.T-1
nuclear magneton, eh/2mp	mN	5.0507866(17) x 10-27 J.T-1
gyromagnetic ratio of proton	gp	2.67522128(81) x 108 s-1.T-1
	gp/2p	4.2577469(13) x 107 Hz.T-1
(proton in pure H2O)*	g'p	2.67515255(81) x 108 s-1.T-1
	g'p/2p	4.2576375(13) x 107 Hz.T-1
magnetic flux quantum, h/2e	F0	2.06783461(61) x 10-15 V.s
magnetic moment of electron	me	9.2847701(31) x 10-24 J.T-1
in terms of Bohr magneton	me/mB	1.001159652193(10)
magneton magnetic moment of proton	mp	1.41060761(47) x 10-26 J.T-1
in terms of Bohr magneton	mp/mB	1.521032202(15) x 10-3
(proton in pure H2O)*	mp'/mB	1.520993129(17) x 10-3
in terms of nuclear magneton	mp/mN	2.792847386(63)