Fundamental Physical Constants

CODATA recommended values — the building blocks of every equation in physics. Filter by category or search by name.

Constant	Symbol	Value	Unit	Category
Speed of light in vacuum exact	c	299 792 458	m/s	Universal
Gravitational constant	G	6.674 30 × 10⁻¹¹	m³/(kg·s²)	Universal
Planck constant exact	h	6.626 070 15 × 10⁻³⁴	J·s	Quantum
Reduced Planck constant exact	ℏ	1.054 571 817 × 10⁻³⁴	J·s	Quantum
Elementary charge exact	e	1.602 176 634 × 10⁻¹⁹	C	Electromagnetic
Boltzmann constant exact	k_B	1.380 649 × 10⁻²³	J/K	Thermodynamic
Avogadro constant exact	N_A	6.022 140 76 × 10²³	mol⁻¹	Thermodynamic
Electron mass	m_e	9.109 383 7015 × 10⁻³¹	kg	Atomic
Proton mass	m_p	1.672 621 923 69 × 10⁻²⁷	kg	Atomic
Neutron mass	m_n	1.674 927 498 04 × 10⁻²⁷	kg	Atomic
Fine-structure constant	α	7.297 352 5693 × 10⁻³	dimensionless	Electromagnetic
Vacuum permittivity	ε₀	8.854 187 8128 × 10⁻¹²	F/m	Electromagnetic
Vacuum permeability	μ₀	1.256 637 062 12 × 10⁻⁶	N/A²	Electromagnetic
Stefan–Boltzmann constant exact	σ	5.670 374 419 × 10⁻⁸	W/(m²·K⁴)	Thermodynamic
Wien displacement constant exact	b	2.897 771 955 × 10⁻³	m·K	Thermodynamic
Rydberg constant	R_∞	10 973 731.568 160	m⁻¹	Atomic
Bohr radius	a₀	5.291 772 109 03 × 10⁻¹¹	m	Atomic
Compton wavelength	λ_C	2.426 310 238 67 × 10⁻¹²	m	Quantum
Magnetic flux quantum exact	Φ₀	2.067 833 848 × 10⁻¹⁵	Wb	Quantum
Electron volt exact	eV	1.602 176 634 × 10⁻¹⁹	J	Universal
Atomic mass unit	u	1.660 539 066 60 × 10⁻²⁷	kg	Atomic
Hubble constant	H₀	67.4 ± 0.5	km/(s·Mpc)	Cosmological
Cosmological constant	Λ	~1.1 × 10⁻⁵²	m⁻²	Cosmological
Planck length	l_P	1.616 255 × 10⁻³⁵	m	Quantum
Planck mass	m_P	2.176 434 × 10⁻⁸	kg	Quantum
Planck temperature	T_P	1.416 784 × 10³²	K	Quantum
Solar neutrino flux (at Earth)	Φ_ν	~6.5 × 10¹⁰	cm⁻²·s⁻¹	Cosmological

Values from CODATA 2018 (NIST). Constants marked "exact" are defined values in the 2019 SI redefinition.

Fundamental Physical Constants

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