List of physical constants

Symbol	Quantity	Value[1]	Relative standard uncertainty	Group
${\displaystyle c}$	speed of light in vacuum	299792458 m⋅s−1[2]	0	ud
${\displaystyle h}$	Planck constant	6.62607015×10−34 J⋅s[3]	0	ud   f
${\displaystyle \hbar =h/2\pi }$	reduced Planck constant	1.054571817...×10−34 J⋅s[4]	0	ud   f
${\displaystyle G}$	Newtonian constant of gravitation	6.67430(15)×10−11 m3⋅kg−1⋅s−2[5]	2.2×10−5	u    f
${\displaystyle \varepsilon _{0}=1/\mu _{0}c^{2}}$	vacuum electric permittivity	8.8541878128(13)×10−12 F⋅m−1[6]	1.5×10−10	u    f
${\displaystyle \mu _{0}}$	vacuum magnetic permeability	1.25663706212(19)×10−6 N⋅A−2[7]	1.5×10−10	u    f
${\displaystyle Z_{0}=\mu _{0}c}$	characteristic impedance of vacuum	376.730313668(57) Ω[8]	1.5×10−10	u
${\displaystyle e,q_{\text{e}}}$	elementary charge	1.602176634×10−19 C[9]	0	de  f
${\displaystyle \Delta \nu _{\text{Cs}}}$	hyperfine transition frequency of 133Cs	9192631770 Hz[10]	0	d
${\displaystyle N_{\text{A}},L}$	Avogadro constant	6.02214076×1023 mol−1[11]	0	d  pf
${\displaystyle k,k_{\text{B}}}$	Boltzmann constant	1.380649×10−23 J⋅K−1[12]	0	d  pf
${\displaystyle G_{0}=2e^{2}/h}$	conductance quantum	7.748091729...×10−5 S[13]	0	e  f
${\displaystyle K_{\mathrm {J} }=2e/h}$	Josephson constant	483597.8484...×109 Hz⋅V−1[14]	0	e  f
${\displaystyle R_{\mathrm {K} }=h/e^{2}}$	von Klitzing constant	25812.80745... Ω[15]	0	e  f
${\displaystyle \Phi _{0}=h/2e}$	magnetic flux quantum	2.067833848...×10−15 Wb[16]	0	e  f
${\displaystyle G_{0}^{-1}=h/2e^{2}}$	inverse conductance quantum	12906.40372... Ω[17]	0	e
${\displaystyle \mu _{\mathrm {B} }=e\hbar /2m_{\mathrm {e} }}$	Bohr magneton	9.2740100783(28)×10−24 J⋅T−1[18]	3.0×10−10	e
${\displaystyle \mu _{\mathrm {N} }=e\hbar /2m_{\mathrm {p} }}$	nuclear magneton	5.0507837461(15)×10−27 J⋅T−1[19]	3.1×10−10	e
${\displaystyle \alpha =e^{2}/4\pi \varepsilon _{0}\hbar c}$	fine-structure constant	7.2973525693(11)×10−3[20]	1.5×10−10	a f
${\displaystyle \alpha ^{-1}}$	inverse fine-structure constant	137.035999084(21)[21]	1.5×10−10	a f
${\displaystyle m_{\mathrm {e} }}$	electron mass	9.1093837015(28)×10−31 kg[22]	3.0×10−10	a f
${\displaystyle m_{\mathrm {p} }}$	proton mass	1.67262192369(51)×10−27 kg[23]	3.1×10−10	a f
${\displaystyle m_{\mathrm {n} }}$	neutron mass	1.67492749804(95)×10−27 kg[24]	5.7×10−10	a
${\displaystyle a_{0}=\hbar /\alpha m_{\text{e}}c}$	Bohr radius	5.29177210903(80)×10−11 m[25]	1.5×10−10	a
${\displaystyle r_{\mathrm {e} }=e^{2}/4\pi \varepsilon _{0}m_{\mathrm {e} }c^{2}}$	classical electron radius	2.8179403262(13)×10−15 m[26]	4.5×10−10	a
${\displaystyle g_{\mathrm {e} }}$	electron g-factor	−2.00231930436256(35)[27]	1.7×10−13	a
${\displaystyle G_{\mathrm {F} }/(\hbar c)^{3}}$	Fermi coupling constant	1.1663787(6)×10−5 GeV−2[28]	5.1×10−7	a
${\displaystyle E_{\mathrm {h} }=2R_{\infty }hc}$	Hartree energy	4.3597447222071(85)×10−18 J[29]	1.9×10−12	a
${\displaystyle h/2m_{\mathrm {e} }}$	quantum of circulation	3.6369475516(11)×10−4 m2⋅s−1[30]	3.0×10−10	a
${\displaystyle R_{\infty }=\alpha ^{2}m_{\mathrm {e} }c/2h}$	Rydberg constant	10973731.568160(21) m−1[31]	1.9×10−12	a
${\displaystyle \sigma _{\text{e}}=(8\pi /3)r_{\mathrm {e} }^{2}}$	Thomson cross section	6.6524587321(60)×10−29 m2[32]	9.1×10−10	a
${\displaystyle m_{\mathrm {W} }/m_{\mathrm {Z} }}$	W-to-Z mass ratio	0.88153(17)[33]	1.9×10−4
${\displaystyle \sin ^{2}\theta _{\mathrm {W} }=1-(m_{\mathrm {W} }/m_{\mathrm {Z} })^{2}}$	weak mixing angle	0.22290(30)[34]	1.3×10−3	a
${\displaystyle m_{\text{u}}=1\,{\text{Da}}}$	atomic mass constant	1.66053906660(50)×10−27 kg[35]	3.0×10−10	pf
${\displaystyle F=N_{\text{A}}e}$	Faraday constant	96485.33212... C⋅mol−1[36]	0	pf
${\displaystyle R=N_{\text{A}}k_{\text{B}}}$	molar gas constant	8.314462618... J⋅mol−1⋅K−1[37]	0	pf
${\displaystyle M_{\text{u}}=M({}^{12}{\text{C}})/12}$	molar mass constant	0.99999999965(30)×10−3 kg⋅mol−1[38]	3.0×10−10	pf
${\displaystyle \sigma =\pi ^{2}k^{4}/60\hbar ^{3}c^{2}}$	Stefan–Boltzmann constant	5.670374419...×10−8 W⋅m−2⋅K−4[39]	0	pf
${\displaystyle c_{1}=2\pi hc^{2}}$	first radiation constant	3.741771852...×10−16 W⋅m2[40]	0	p
${\displaystyle c_{\text{1L}}=c_{1}/\pi }$	first radiation constant for spectral radiance	1.191042972...×10−16 W⋅m2⋅sr−1[41]	0	p
${\displaystyle M({}^{12}{\text{C}})=N_{\text{A}}m({}^{12}{\text{C}})}$	molar mass of carbon-12	11.9999999958(36)×10−3 kg⋅mol−1[42]	3.0×10−10	p
${\displaystyle N_{\text{A}}h}$	molar Planck constant	3.990312712...×10−10 J⋅Hz−1⋅mol−1[43]	0	p
${\displaystyle c_{2}=hc/k}$	second radiation constant	1.438776877...×10−2 m⋅K[44]	0	p
${\displaystyle b}$	Wien wavelength displacement law constant	2.897771955...×10−3 m⋅K[45]	0	p
${\displaystyle b'}$	Wien frequency displacement law constant	5.878925757...×1010 Hz⋅K−1[46]	0	p
${\displaystyle b_{\text{entropy}}}$	Wien entropy displacement law constant	3.002916077...×10−3 m⋅K[47]	0	p

'Group' reflects categorization on the NIST website:[48]

There are some notable omissions in the site's classification: the speed of light (f), vacuum electric permittivity (e), vacuum magnetic permeability (e), hyperfine transition frequency of ¹³³Cs (p).

• Physical constant