PhysRefPhysics reference
Constants

27 physical constants

Universal, electromagnetic, atomic, thermodynamic, Earth, and practical constants.

Physical constants follow the CODATA 2018 recommended values published by NIST. The astronomical unit and the light-year are exact by IAU definition. The Earth, Sun and practical rows are measured reference values. Measured values are shown rounded.

27 constants

Universal4 constants

Speed of Light in Vacuum

Universal
299,792,458
m/s

Exact by definition

299792458

Gravitational Constant

Universal
6.674 30 × 10⁻¹¹
N·m²/kg²

Measured (CODATA 2018), ± 0.000 15 × 10⁻¹¹ N·m²/kg²

6.67430e-11

Planck Constant

Universal
6.626 070 15 × 10⁻³⁴
J·s

Exact by definition

6.62607015e-34

Reduced Planck Constant

Universal
1.054 571 817… × 10⁻³⁴
J·s

Exact by definition

1.054571817e-34

Electromagnetic4 constants

Elementary Charge

Electromagnetic
1.602 176 634 × 10⁻¹⁹
C

Exact by definition

1.602176634e-19

Coulomb Constant

Electromagnetic
8.988 × 10⁹
N·m²/C²

Measured (from CODATA 2018 ε₀)

8.988e9

Vacuum Permittivity

Electromagnetic
8.854 × 10⁻¹²
F/m

Measured (CODATA 2018)

8.854e-12

Vacuum Permeability

Electromagnetic
1.257 × 10⁻⁶
H/m

Measured (CODATA 2018)

1.257e-6

Atomic6 constants

Electron Mass

Atomic
9.109 × 10⁻³¹
kg

Measured (CODATA 2018)

9.109e-31

Proton Mass

Atomic
1.673 × 10⁻²⁷
kg

Measured (CODATA 2018)

1.673e-27

Neutron Mass

Atomic
1.675 × 10⁻²⁷
kg

Measured (CODATA 2018)

1.675e-27

Atomic Mass Unit

Atomic
1.661 × 10⁻²⁷
kg

Measured (CODATA 2018)

1.661e-27

Bohr Radius

Atomic
5.292 × 10⁻¹¹
m

Measured (CODATA 2018)

5.292e-11

Rydberg Constant

Atomic
1.097 × 10⁷
m⁻¹

Measured (CODATA 2018)

1.097e7

Thermodynamic4 constants

Boltzmann Constant

Thermodynamic
1.380 649 × 10⁻²³
J/K

Exact by definition

1.380649e-23

Molar Gas Constant

Thermodynamic
8.314 462 618…
J/(mol·K)

Exact by definition

8.314462618

Avogadro Constant

Thermodynamic
6.022 140 76 × 10²³
mol⁻¹

Exact by definition

6.02214076e23

Stefan-Boltzmann Constant

Thermodynamic
5.670 374 419… × 10⁻⁸
W/(m²·K⁴)

Exact by definition

5.670374419e-8

Earth6 constants

Standard Gravity

Earth
9.806 65
m/s²

Exact by definition

9.80665

Earth Mass

Earth
5.972 × 10²⁴
kg

Measured

5.972e24

Earth Radius (mean)

Earth
6.371 × 10⁶
m

Measured

6.371e6

Solar Mass

Earth
1.988 × 10³⁰
kg

Measured (IAU 2015 GM☉ ÷ CODATA 2018 G)

1.988e30

Astronomical Unit

Earth
149 597 870 700
m

Exact by definition (IAU)

149597870700

Light Year

Earth
9 460 730 472 580 800
m

Exact by definition (IAU)

9460730472580800

Other3 constants

Standard Atmosphere

Other
101,325
Pa

Exact by definition

101325

Speed of Sound (air, 20°C)

Other
343
m/s

Measured

Water Density (4°C)

Other
1000
kg/m³

Measured