List of physical constants

The constants listed here are known values of physical constants expressed in SI units; that is, physical quantities that are generally believed to be universal in nature and thus are independent of the unit system in which they are measured. Many of these are redundant, in the sense that they obey a known relationship with other physical constants and can be determined from them.

Table of physical constants

Symbol	Quantity	ValueTemplate:EfnTemplate:Efn	RelativeTemplate:BrstandardTemplate:Bruncertainty	RefTemplate:Refn
$c$	speed of light in vacuum	Template:Physconst	Template:Physconst	Template:Physconst
$h$	Planck constant	Template:Physconst	Template:Physconst	Template:Physconst
$\hslash =h/2\pi$	reduced Planck constant	Template:Physconst	Template:Physconst	Template:Physconst
$k,k_{\text{B}}$	Boltzmann constant	Template:Physconst	Template:Physconst	Template:Physconst
$G$	Newtonian constant of gravitation	Template:Physconst	Template:Physconst	Template:Physconst
$\mathrm{\Lambda }$	cosmological constant	Template:ValTemplate:Px2Template:EfnTemplate:BrTemplate:ValTemplate:Px2Template:Efn	Template:ValTemplate:BrTemplate:Val	Template:Br
$\sigma ={\pi }^2{k}_{\text{B}}^4/60{\hslash }^3{c}^2$	Stefan–Boltzmann constant	Template:Physconst	Template:Physconst	Template:Physconst
$c_1=2\pi h{c}^2$	first radiation constant	Template:Physconst	Template:Physconst	Template:Physconst
$c_{\text{1L}}=2h{c}^2/\mathrm{s}\mathrm{r}$	first radiation constant for spectral radiance	Template:Physconst	Template:Physconst	Template:Physconst
$c_2=hc/k_{\text{B}}$	second radiation constant	Template:Physconst	Template:Physconst	Template:Physconst
$b$Template:Px2Template:Efn	Wien wavelength displacement law constant	Template:Physconst	Template:Physconst	Template:Physconst
$b^{\prime }$Template:Px2Template:Efn	Wien frequency displacement law constant	Template:Physconst	Template:Physconst	Template:Physconst
$b_{\text{entropy}}$	Wien entropy displacement law constant	Template:Val	Template:Val
$e$	elementary charge	Template:Physconst	Template:Physconst	Template:Physconst
$G_0=2e^2/h$	conductance quantum	Template:Physconst	Template:Physconst	Template:Physconst
$G_0^{-1}=h/2e^2$	inverse conductance quantum	Template:Physconst	Template:Physconst	Template:Physconst
$R_{\text{K}}=h/e^2$	von Klitzing constant	Template:Physconst	Template:Physconst	Template:Physconst
$K_{\text{J}}=2e/h$	Josephson constant	Template:Physconst	Template:Physconst	Template:Physconst
${\mathrm{\Phi }}_0=h/2e$	magnetic flux quantum	Template:Physconst	Template:Physconst	Template:Physconst
$\alpha =e^2/4\pi {\epsilon }_0\hslash c$	fine-structure constant	Template:Physconst	Template:Physconst	Template:Physconst
${\alpha }^{-1}$	inverse fine-structure constant	Template:Physconst	Template:Physconst	Template:Physconst
${\mu }_0=4\pi \alpha \hslash /e^{2}c$	vacuum magnetic permeability	Template:Physconst	Template:Physconst	Template:Physconst
$Z_0=4\pi \alpha \hslash /e^2$	characteristic impedance of vacuum	Template:Physconst	Template:Physconst	Template:Physconst
${\epsilon }_0=e^2/4\pi \alpha \hslash c$	vacuum electric permittivity	Template:Physconst	Template:Physconst	Template:Physconst
$m_{\text{e}}$	electron mass	Template:Physconst	Template:Physconst	Template:Physconst
$m_{\mu }$	muon mass	Template:Physconst	Template:Physconst	Template:Physconst
$m_{\tau }$	tau mass	Template:Physconst	Template:Physconst	Template:Physconst
$m_{\text{p}}$	proton mass	Template:Physconst	Template:Physconst	Template:Physconst
$m_{\text{n}}$	neutron mass	Template:Physconst	Template:Physconst	Template:Physconst
$m_{\text{p}}/m_{\text{e}}$	proton-to-electron mass ratio	Template:Physconst	Template:Physconst	Template:Physconst
$m_{\text{W}}/m_{\text{Z}}$	W-to-Z mass ratio	Template:Physconst	Template:Physconst	Template:Physconst
${\sin }^2{\theta }_{\text{W}}$ $=1-(m_{\text{W}}/m_{\text{Z}}{)}^2$	sine-square weak mixing angle	Template:PhysconstTemplate:Px2Template:EfnTemplate:BrTemplate:ValTemplate:Px2Template:EfnTemplate:BrTemplate:ValTemplate:Px2Template:Efn	Template:PhysconstTemplate:BrTemplate:ValTemplate:BrTemplate:Val	Template:PhysconstTemplate:BrTemplate:Br
$g_{\text{e}}$	electron g-factor	Template:Physconst	Template:Physconst	Template:Physconst
$g_{\mu }$	muon g-factor	Template:Physconst	Template:Physconst	Template:Physconst
$g_{\text{p}}$	proton g-factor	Template:Physconst	Template:Physconst	Template:Physconst
$h/2m_{\text{e}}$	quantum of circulation	Template:Physconst	Template:Physconst	Template:Physconst
${\mu }_{\text{B}}=e\hslash /2m_{\text{e}}$	Bohr magneton	Template:Physconst	Template:Physconst	Template:Physconst
${\mu }_{\text{N}}=e\hslash /2m_{\text{p}}$	nuclear magneton	Template:Physconst	Template:Physconst	Template:Physconst
$r_{\text{e}}=\alpha \hslash /m_{\text{e}}c$	classical electron radius	Template:Physconst	Template:Physconst	Template:Physconst
${\sigma }_{\text{e}}=(8\pi /3)r_{\text{e}}^2$	Thomson cross section	Template:Physconst	Template:Physconst	Template:Physconst
$a_0=\hslash /\alpha m_{\text{e}}c$	Bohr radius	Template:Physconst	Template:Physconst	Template:Physconst
$R_{\mathrm{\infty }}={\alpha }^2{m}_{\text{e}}c/2h$	Rydberg constant	Template:Physconst	Template:Physconst	Template:Physconst
$\mathrm{R}\mathrm{y}=R_{\mathrm{\infty }}hc=E_{\text{h}}/2$	Rydberg unit of energy	Template:Physconst	Template:Physconst	Template:Physconst
$E_{\text{h}}={\alpha }^2{m}_{\text{e}}{c}^2$	Hartree energy	Template:Physconst	Template:Physconst	Template:Physconst
$G_{\text{F}}/(\hslash c{)}^3$	Fermi coupling constant	Template:Physconst	Template:Physconst	Template:Physconst
$N_{\text{A}}$	Avogadro constant	Template:Physconst	Template:Physconst	Template:Physconst
$R=N_{\text{A}}{k}_{\text{B}}$	molar gas constant	Template:Val	Template:Physconst	Template:Physconst
$F=N_{\text{A}}e$	Faraday constant	Template:Val	Template:Physconst	Template:Physconst
$N_{\text{A}}h$	molar Planck constant	Template:Val	Template:Physconst	Template:Physconst
$M({}^{12}\text{C})=N_{\text{A}}m({}^{12}\text{C})$	molar mass of carbon-12	Template:Physconst	Template:Physconst	Template:Physconst
$m_{\text{u}}=m({}^{12}\text{C})/12$	atomic mass constant	Template:Physconst	Template:Physconst	Template:Physconst
$M_{\text{u}}=M({}^{12}\text{C})/12$	molar mass constant	Template:Physconst	Template:Physconst	Template:Physconst
$V_{\text{m}}(\text{Si})$	molar volume of silicon	Template:Physconst	Template:Physconst	Template:Physconst
$\mathrm{\Delta }{\nu }_{\text{Cs}}$	hyperfine transition frequency of 133Cs	Template:Physconst	Template:Physconst	Template:Physconst

Uncertainties

While the values of the physical constants are independent of the system of units in use, each uncertainty as stated reflects our lack of knowledge of the corresponding value as expressed in SI units, and is strongly dependent on how those units are defined. For example, the atomic mass constant $m_{\text{u}}$ is exactly known when expressed using the dalton (its value is exactly 1 Da), but the kilogram is not exactly known when using these units, the opposite of when expressing the same quantities using the kilogram.

Technical constants

Some of these constants are of a technical nature and do not give any true physical property, but they are included for convenience. Such a constant gives the correspondence ratio of a technical dimension with its corresponding underlying physical dimension. These include the Boltzmann constant $k_{\text{B}}$, which gives the correspondence of the dimension temperature to the dimension of energy per degree of freedom, and the Avogadro constant $N_{\text{A}}$, which gives the correspondence of the dimension of amount of substance with the dimension of count of entities (the latter formally regarded in the SI as being dimensionless). By implication, any product of powers of such constants is also such a constant, such as the molar gas constant $R$.

See also

• List of mathematical constants
• Mathematical constant
• Physical constant
• List of particles