| Universal |
|---|
| speed of light in vacuum | c | | m s−1 | exact |
| vacuum magnetic permeability4παℏ/e2c | μ0 | | N A−2 | 1.6 × 10−10 |
| vacuum electric permittivity1/μ0c2 | ε0 | | F m−1 | 1.6 × 10−10 |
| Newtonian constant of gravitation | G | | m3 kg−1 s−2 | 2.2 × 10−5 |
| Planck constant | h | | J Hz−1 | exact |
| reduced Planck constanth/2π | ℏ | | J s | exact |
| Planck length(ℏG/c3)1/2 | lP | | m | 1.1 × 10−5 |
| Planck mass(ℏc/G)1/2 | mP | | kg | 1.1 × 10−5 |
| Planck time(ℏG/c5)1/2 | tP | | s | 1.1 × 10−5 |
| Planck temperature(ℏc5/G)1/2/k | TP | | K | 1.1 × 10−5 |
| Electromagnetic |
|---|
| elementary charge | e | | C | exact |
| magnetic flux quantumh/2e | Φ0 | | Wb | exact |
| conductance quantum2e2/h | G0 | | S | exact |
| Josephson constant2e/h | KJ | | Hz V−1 | exact |
| von Klitzing constanth/e2 | RK | | Ω | exact |
| Bohr magnetoneℏ/2me | μB | | J T−1 | 3.1 × 10−10 |
| nuclear magnetoneℏ/2mp | μN | | J T−1 | 3.1 × 10−10 |
| electron charge-to-mass quotient | −e/me | | C kg−1 | 3.1 × 10−10 |
| Atomic & nuclear |
|---|
| fine-structure constante2/4πε0ℏc | α | | | 1.6 × 10−10 |
| inverse fine-structure constant | α−1 | | | 1.6 × 10−10 |
| Rydberg constantα2mec/2h | R∞ | | m−1 | 1.1 × 10−12 |
| Rydberg energy | R∞hc | | eV | 1.1 × 10−12 |
| Bohr radiusℏ/αmec | a0 | | m | 1.6 × 10−10 |
| Hartree energy2R∞hc | Eh | | J | 1.1 × 10−12 |
| electron mass | me | | kg | 3.1 × 10−10 |
| electron rest energy | mec2 | | MeV | 3.1 × 10−10 |
| electron g-factor | ge | | | 1.8 × 10−13 |
| Compton wavelengthh/mec | λC | | m | 3.1 × 10−10 |
| classical electron radiusα2a0 | re | | m | 4.7 × 10−10 |
| Thomson cross section(8π/3)re2 | σe | | m2 | 9.3 × 10−10 |
| proton mass | mp | | kg | 3.1 × 10−10 |
| proton rest energy | mpc2 | | MeV | 3.1 × 10−10 |
| proton-electron mass ratio | mp/me | | | 1.7 × 10−11 |
| proton rms charge radius | rp | | m | 7.6 × 10−4 |
| neutron mass | mn | | kg | 5.1 × 10−10 |
| neutron rest energy | mnc2 | | MeV | 5.1 × 10−10 |
| deuteron mass | md | | kg | 3.1 × 10−10 |
| alpha particle mass | mα | | kg | 3.1 × 10−10 |
| muon mass | mμ | | kg | 2.2 × 10−8 |
| tau mass | mτ | | kg | 6.8 × 10−5 |
| Fermi coupling constant | GF/(ℏc)3 | | GeV−2 | 5.1 × 10−7 |
| weak mixing angle | sin2θW | | | 1.0 × 10−3 |
| Physicochemical |
|---|
| Avogadro constant | NA | | mol−1 | exact |
| Faraday constantNAe | F | | C mol−1 | exact |
| molar gas constantNAk | R | | J mol−1 K−1 | exact |
| Boltzmann constantR/NA | k | | J K−1 | exact |
| Stefan–Boltzmann constant(π2/60)k4/ℏ3c2 | σ | | W m−2 K−4 | exact |
| molar volume of ideal gas273.15 K, 101.325 kPa | Vm | | m3 mol−1 | exact |
| Wien displacement law constantλmaxT | b | | m K | exact |
| second radiation constanthc/k | c2 | | m K | exact |
| Adopted & non-SI |
|---|
| electron volt(e/C) J | eV | | J | exact |
| (unified) atomic mass unit1⁄12m(12C) | u | | kg | 3.1 × 10−10 |
| atomic mass unit rest energy | muc2 | | MeV | 3.1 × 10−10 |
| standard acceleration of gravity | gn | | m s−2 | exact |
| standard atmosphere | atm | | Pa | exact |