ConstantID

CODATA 2022 · 355 constants · checked weekly against NIST

Every physical constant, identified.

Values and uncertainties exactly as NIST publishes them, how each one changed since 1998, what it means, and the value ready to paste into your calculation.

The constants people look up most

UniversalElectromagneticAtomic & nuclearPhysico-chemicalUnitsAdopted

Universal G Gravitational constant 6.674 30(15) × 10−11 m3 kg−1 s−2 Universal exact h Planck constant 6.626 070 15 × 10−34 J Hz−1 Universal exact ℏ Reduced Planck constant 1.054 571 817… × 10−34 J s Universal exact c Speed of light 299 792 458 m s−1 Universal ε0 Electric constant 8.854 187 8188(14) × 10−12 F m−1 Universal μ0 Magnetic constant 1.256 637 061 27(20) × 10−6 N A−2 Electromagnetic μB Bohr magneton 9.274 010 0657(29) × 10−24 J T−1 Electromagnetic exact e Elementary charge 1.602 176 634 × 10−19 C Electromagnetic exact KJ Josephson constant 483 597.8484… × 109 Hz V−1 Electromagnetic exact RK von Klitzing constant 25 812.807 45… Ω Atomic & nuclear a0 Bohr radius 5.291 772 105 44(82) × 10−11 m Atomic & nuclear me Electron mass 9.109 383 7139(28) × 10−31 kg Atomic & nuclear α Fine-structure constant 7.297 352 5643(11) × 10−3 Atomic & nuclear Eh Hartree energy 4.359 744 722 2060(48) × 10−18 J Atomic & nuclear mn Neutron mass 1.674 927 500 56(85) × 10−27 kg Atomic & nuclear mp Proton mass 1.672 621 925 95(52) × 10−27 kg Atomic & nuclear R∞ Rydberg constant 10 973 731.568 157(12) m−1 Physico-chemical exact NA Avogadro constant 6.022 140 76 × 1023 mol−1 Physico-chemical exact k Boltzmann constant 1.380 649 × 10−23 J K−1 Physico-chemical exact F Faraday constant 96 485.332 12… C mol−1 Physico-chemical exact R Gas constant 8.314 462 618… J mol−1 K−1 Physico-chemical exact σ Stefan–Boltzmann 5.670 374 419… × 10−8 W m−2 K−4 Physico-chemical exact b Wien constant 2.897 771 955… × 10−3 m K Units exact eV Electron volt 1.602 176 634 × 10−19 J

All 355 constants, searchable →

The seven constants that define the SI

How the 2019 redefinition works →

  1. ΔνCsdefines the second9 192 631 770 Hz
  2. cdefines the metre299 792 458 m s−1
  3. hdefines the kilogram6.626 070 15 × 10−34 J Hz−1
  4. edefines the ampere1.602 176 634 × 10−19 C
  5. kdefines the kelvin1.380 649 × 10−23 J K−1
  6. NAdefines the mole6.022 140 76 × 1023 mol−1
  7. Kcddefines the candela683 lm W−1

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Universal constantsThe speed of light, the Planck constant, gravity and the constants of empty space: the ones that do not belong to any one particle.16 constants Electromagnetic constantsThe elementary charge, magnetons, the quantum standards of voltage and resistance, and the 1990 conventional electrical units.26 constants Atomic and nuclear constantsMasses, magnetic moments, radii and ratios for the electron, muon, tau, proton, neutron and light nuclei, plus α, R∞ and the Bohr radius.186 constants Physico-chemical constantsAvogadro, Boltzmann, the gas constant, Faraday, black-body radiation and the molar quantities chemists use.25 constants Atomic, natural and X-ray unitsAtomic units, natural units, the electron volt, the dalton and X-ray length units, with their SI values.42 constants Adopted valuesValues fixed by agreement rather than measured: the seven SI defining constants and conventions such as standard gravity and the standard atmosphere.11 constants

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Max PlanckMax PlanckLudwig BoltzmannLudwig BoltzmannAmedeo AvogadroAmedeo AvogadroMichael FaradayMichael FaradayJohannes RydbergJohannes RydbergNiels BohrNiels BohrDouglas HartreeDouglas HartreeBrian JosephsonBrian Josephson