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CODATA Fundamental Physical Constants Explorer

Explore fundamental physical constants from NIST CODATA 2022 including speed of light, Planck constant, gravitational constant, Avogadro number, electron mass, and vacuum permittivity with search and instant copy.

CODATA Fundamental Physical Constants Reference

NIST CODATA 2022 recommended international fundamental physical constants with exact definitions and 1-click copy

cExact (SI Defined)

Speed of Light in Vacuum

Speed of all electromagnetic waves in vacuum

299792458 m/s

hExact (SI Defined)

Planck's Constant

Quantum of electromagnetic action

6.62607015e-34 J·s

ħExact (SI Defined)

Reduced Planck Constant (h / 2π)

Dirac constant in quantum mechanics

1.054571817e-34 J·s

GExperimental

Newtonian Gravitational Constant

Universal constant of gravitation

6.67430e-11 m³/(kg·s²)

Uncertainty: ±0.00015e-11

eExact (SI Defined)

Elementary Charge

Electric charge carried by a single proton

1.602176634e-19 C

ε₀Experimental

Vacuum Electric Permittivity

Permittivity of free space

8.8541878128e-12 F/m

Uncertainty: ±0.0000000013e-12

μ₀Experimental

Vacuum Magnetic Permeability

Permeability of free space

1.25663706212e-6 N/A²

Uncertainty: ±0.00000000019e-6

k_eExperimental

Coulomb's Constant (1 / 4πε₀)

Electrostatic force constant

8.9875517923e9 N·m²/C²

Φ₀Exact (SI Defined)

Magnetic Flux Quantum (h / 2e)

Quantum of magnetic flux in superconductors

2.067833848e-15 Wb

m_eExperimental

Electron Mass

Rest mass of an electron

9.1093837015e-31 kg

Uncertainty: ±0.0000000028e-31

m_pExperimental

Proton Mass

Rest mass of a proton

1.67262192369e-27 kg

Uncertainty: ±0.00000000051e-27

m_nExperimental

Neutron Mass

Rest mass of a free neutron

1.67492749804e-27 kg

Uncertainty: ±0.00000000095e-27

uExperimental

Unified Atomic Mass Unit (Dalton)

One twelfth of the mass of Carbon-12

1.66053906660e-27 kg

Uncertainty: ±0.00000000050e-27

αExperimental

Fine-Structure Constant

Electromagnetic interaction strength

7.2973525693e-3 dimensionless (≈ 1/137.036)

Uncertainty: ±0.0000000011e-3

R_∞Experimental

Rydberg Constant

Atomic spectral line limiting wave number

10973731.568160 m⁻¹

Uncertainty: ±0.000021

a₀Experimental

Bohr Radius

Radius of ground state orbit of electron in hydrogen

5.29177210903e-11 m

Uncertainty: ±0.00000000080e-11

N_AExact (SI Defined)

Avogadro's Constant

Number of constituent particles in one mole

6.02214076e23 mol⁻¹

k_BExact (SI Defined)

Boltzmann's Constant

Relates average kinetic energy of gas to temperature

1.380649e-23 J/K

RExact (SI Defined)

Universal Gas Constant (N_A · k_B)

Molar gas constant in ideal gas law

8.314462618 J/(mol·K)

σExact (SI Defined)

Stefan-Boltzmann Constant

Blackbody radiation power constant

5.670374419e-8 W/(m²·K⁴)

FExact (SI Defined)

Faraday Constant (N_A · e)

Electric charge per mole of electrons

96485.33212 C/mol

What are Fundamental Physical Constants?

Fundamental physical constants are universal invariant quantities in physics that define the foundations of modern scientific laws and the International System of Units (SI).

The Committee on Data for Science and Technology (CODATA) periodically analyzes all international experimental data to provide the internationally accepted recommended values for these constants.

Formula & Step-by-Step Calculation

c, h, \hbar, G, k_B, N_A, e, m_e, m_p, m_n, \epsilon_0, \mu_0, R, \sigma, \alpha, a_0, R_\infty

CODATA 2022 internationally accepted exact SI defining constants and experimental best estimates.

Worked Step-by-Step Examples

Example 1

What is Planck's Constant in SI units and electron-volts?

Solution: h = 6.626 070 15 × 10⁻³⁴ J·s = 4.135 667 696... × 10⁻¹⁵ eV·s (Exact by 2019 SI definition)

• SI definition: h = 6.626 070 15 × 10⁻³⁴ J·s exactly.

• Dividing by elementary charge e = 1.602 176 634 × 10⁻¹⁹ C gives 4.135 667 696 × 10⁻¹⁵ eV·s.

Common Real-World & Academic Use Cases

✓ Quick verification of exact physical constants for homework and research
✓ Quantum mechanics and relativistic physics calculations
✓ Electromagnetic wave and photon energy computations
✓ Thermodynamics and statistical mechanics modeling

How to Use the CODATA Fundamental Physical Constants Explorer

Filter by Category

Browse Universal, Electromagnetic, Atomic & Nuclear, or Physico-Chemical constants.

Search by Keyword or Symbol

Type 'speed of light', 'hbar', 'boltzmann', or 'G' into the instant filter bar.

Copy Exact Value

Click any value to copy either the exact floating number or scientific notation string directly to your clipboard.

Frequently Asked Questions

Q: Why do some constants have zero uncertainty?

Since the 2019 redefinition of the SI base units, constants like the speed of light (c), Planck's constant (h), elementary charge (e), Boltzmann's constant (kB), and Avogadro's constant (NA) have exact assigned numerical values with zero standard uncertainty.

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