Accumath Toolchest — Physical Constants: Notes

Dataset file: accumath-physical-constants.csv Built: 2026-10-20

Source and edition

Single source for every value: the NIST CODATA "Fundamental Physical Constants — Complete Listing", 2022 CODATA adjustment, official ASCII table at physics.nist.gov/cuu/Constants/Table/allascii.txt (NIST Physical Measurement Laboratory, physics.nist.gov/constants). NIST is a US federal agency; its published reference data is a US government work — public domain. No other source was used, and no value was filled from memory.
The CSV's per-row source column names this table for all 61 rows.
codata_edition is 2022 for every row. If the engine pins constants, it should pin them to this edition as a set — do not mix editions.

Formatting

NIST prints values with spaces as digit-group separators (e.g. 6.644 657 3450 e-27). The CSV strips those grouping spaces (6.6446573450e-27); the digits themselves are unchanged.
Values ending in ... are printed that way by NIST: the constant is exact (or an exact derived product/quotient of exact constants) with a non-terminating decimal expansion. The ... is retained as published.
uncertainty is NIST's standard uncertainty exactly as printed in the table's uncertainty column (grouping spaces stripped). Where NIST prints (exact), the CSV records exact and sets exact_by_definition = yes.

The exact constants and the 2019 SI redefinition

Twenty-four of the 61 rows are exact. The root of that exactness is the 2019 redefinition of the SI (in force 20 May 2019), which fixed the numerical values of seven defining constants:

Defining constant	Fixed value	Defines
Hyperfine transition frequency of Cs-133, Δν_Cs	9 192 631 770 Hz	second
Speed of light in vacuum, c	299 792 458 m s⁻¹	metre
Planck constant, h	6.626 070 15 × 10⁻³⁴ J s	kilogram
Elementary charge, e	1.602 176 634 × 10⁻¹⁹ C	ampere
Boltzmann constant, k	1.380 649 × 10⁻²³ J K⁻¹	kelvin
Avogadro constant, N_A	6.022 140 76 × 10²³ mol⁻¹	mole
Luminous efficacy K_cd (540 THz)	683 lm W⁻¹	candela

Everything else marked exact in the CSV is exact by derivation from those seven — e.g. ħ = h/2π, R = N_A·k, F = N_A·e, σ and the radiation constants (powers of c, h, k), G_0, K_J, R_K, Φ_0 (ratios of h and e), the electron volt, and the Loschmidt constant and molar gas volume (built from N_A, k, and the conventional standard atmosphere). The conventional values g_n = 9.806 65 m s⁻² and 1 atm = 101 325 Pa are exact by long-standing international agreement, independent of the 2019 redefinition.

One change worth knowing: vacuum electric permittivity ε_0 and vacuum magnetic permeability μ_0 are no longer exact. Before 2019 μ_0 was exactly 4π × 10⁻⁷ N A⁻²; under the redefined SI both are measured quantities tied to the fine-structure constant, and CODATA 2022 gives them small but real uncertainties (they are exact_by_definition = no in the CSV). Any code still treating μ_0 as exact is carrying a pre-2019 assumption.

Coverage

61 constants: the 7 SI defining constants; ħ, R, F, ε_0, μ_0, Z_0, G; blackbody constants (σ, Wien b, first/second radiation constants incl. the spectral-radiance form of c_1); atomic and nuclear constants (R_∞ and the Rydberg energy in J and eV, α and 1/α, atomic mass constant in kg and its MeV energy equivalent, Bohr radius, Hartree energy, classical electron radius, Thomson cross section, Bohr and nuclear magnetons, atomic units of time and velocity, quantum of circulation, proton gyromagnetic ratio); quantum electrical standards (G_0, K_J, R_K, Φ_0); particle masses (electron, proton, neutron, deuteron, triton, helion, alpha particle, muon, tau — kg, plus MeV energy equivalents for e/p/n) and the proton–electron and neutron–proton mass ratios; the weak mixing angle; the Sackur–Tetrode constant (1 K, 101.325 kPa form); and the conventional reference values (eV in J, g_n, standard atmosphere, molar volume of an ideal gas at STP, Loschmidt constant).

Dropped — requested but not in the NIST CODATA listing

The following were in the requested scope but do not appear anywhere in the 2022 CODATA complete listing, and no other NIST constants page carrying them could be verified, so they were left out rather than sourced from memory or a third party:

Astronomical unit, light year, parsec, solar mass, Earth mass — astrophysical quantities. NIST's CODATA constants listing does not carry them (their values originate with the IAU and ephemeris work, not the CODATA adjustment). If Accumath wants them, they should come in as their own sourced dataset (e.g. IAU 2012/2015 resolutions), not as CODATA rows.
W and Z boson masses — particle-data quantities maintained by the Particle Data Group; NIST's constants listing carries the weak mixing angle (included, 0.223 05 ± 0.000 23) but not the W/Z masses themselves.

Nothing else in the requested scope was dropped: the Sackur–Tetrode constant and the quantum of circulation, flagged "skip if unavailable", are both in the NIST table and are included.