Physical Constants (CODATA 2022)
These 20 physical constants can be called by name in the calculator. Values are the CODATA 2022 recommended values, sourced from the NIST Reference on Fundamental Physical Constants.
| Symbol | Name | Value | Standard uncertainty | Unit | Input name |
|---|---|---|---|---|---|
| c | Speed of light in vacuum | 299 792 458 | Exact (defined) | m s⁻¹ | c0 |
| h | Planck constant | 6.626 070 15×10⁻³⁴ | Exact (defined) | J Hz⁻¹ | hP |
| ħ | Reduced Planck constant | 1.054 571 817…×10⁻³⁴ | Exact (defined) | J s | hbar |
| e | Elementary charge | 1.602 176 634×10⁻¹⁹ | Exact (defined) | C | qe |
| NA | Avogadro constant | 6.022 140 76×10²³ | Exact (defined) | mol⁻¹ | NA |
| k | Boltzmann constant | 1.380 649×10⁻²³ | Exact (defined) | J K⁻¹ | kB |
| R | Molar gas constant | 8.314 462 618… | Exact (defined) | J mol⁻¹ K⁻¹ | R |
| F | Faraday constant | 96 485.332 12… | Exact (defined) | C mol⁻¹ | F |
| σ | Stefan–Boltzmann constant | 5.670 374 419…×10⁻⁸ | Exact (defined) | W m⁻² K⁻⁴ | sigma |
| gn | Standard acceleration of gravity | 9.806 65 | Exact (defined) | m s⁻² | g0 |
| G | Newtonian constant of gravitation | 6.674 30×10⁻¹¹ | 0.000 15×10⁻¹¹ | m³ kg⁻¹ s⁻² | G |
| me | Electron mass | 9.109 383 7139×10⁻³¹ | 0.000 000 0028×10⁻³¹ | kg | me |
| mp | Proton mass | 1.672 621 925 95×10⁻²⁷ | 0.000 000 000 52×10⁻²⁷ | kg | mp |
| mn | Neutron mass | 1.674 927 500 56×10⁻²⁷ | 0.000 000 000 85×10⁻²⁷ | kg | mn |
| mu | Atomic mass constant | 1.660 539 068 92×10⁻²⁷ | 0.000 000 000 52×10⁻²⁷ | kg | mu |
| ε₀ | Vacuum electric permittivity | 8.854 187 8188×10⁻¹² | 0.000 000 0014×10⁻¹² | F m⁻¹ | eps0 |
| μ₀ | Vacuum magnetic permeability | 1.256 637 061 27×10⁻⁶ | 0.000 000 000 20×10⁻⁶ | N A⁻² | mu0 |
| α | Fine-structure constant | 7.297 352 5643×10⁻³ | 0.000 000 0011×10⁻³ | 1 | alpha |
| a₀ | Bohr radius | 5.291 772 105 44×10⁻¹¹ | 0.000 000 000 82×10⁻¹¹ | m | a0 |
| R∞ | Rydberg constant | 10 973 731.568 157 | 0.000 012 | m⁻¹ | Rinf |
About the values
Since the redefinition of the International System of Units (SI) on 20 May 2019, the speed of light c, the Planck constant h, the elementary charge e, the Boltzmann constant k and the Avogadro constant Nₐ have exactly defined values. Constants derived from them, namely the reduced Planck constant ħ = h/2π, the gas constant R = Nₐk, the Faraday constant F = Nₐe and the Stefan–Boltzmann constant σ, have no uncertainty either (they are non-terminating decimals, so the table shows only the leading digits). The standard acceleration of gravity gₙ = 9.80665 m/s² is a conventional value.
The Newtonian constant of gravitation G, the electron and proton masses, the fine-structure constant α and others are determined by measurement and therefore carry a standard uncertainty. The uncertainty in the table is the 1σ standard uncertainty in the last digits of the value. For example, G = 6.674 30(15)×10⁻¹¹ means 6.674 30 ± 0.000 15 (×10⁻¹¹).
Using them in the calculator
Write the input name directly in an expression. For example, the photon energy E = hc/λ (λ = 500 nm) is hP*c0/500E-9, which gives about 3.973×10⁻¹⁹ J. To convert that to electronvolts, enter Ans/qe (≈ 2.48 eV). All values are plain numbers in SI units, so unit conversions are up to you.
Sources
- NIST, The NIST Reference on Constants, Units, and Uncertainty — CODATA 2022 recommended values (physics.nist.gov/constants), checked 2026-09-24
- Mohr, P. J. et al., CODATA Recommended Values of the Fundamental Physical Constants: 2022, Reviews of Modern Physics (2025)