Physical Constants

Glenn Elert

Physical Constants

Reference

Physical constants (exact, computed, measured) Sources: exact, BIPM; measured, NIST, *NASA

symbol

name

value

c

speed of light in a vacuum

299,792,458 m/s

G

gravitational constant

6.67430 × 10⁻¹¹ N m²/kg²

h

Planck constant

6.62607015 × 10⁻³⁴ J s
4.135667696 × 10⁻¹⁵ eV s

hc

h c

1.98644586 × 10⁻²⁵ J m
1,239.841984 eV nm

ℏ =	h
	2π

h bar,
reduced Planck constant,
Dirac constant

1.054571817 × 10⁻³⁴ J s
6.582119569 × 10⁻¹⁶ eV s

f_Cs

hyperfine transition of ¹³³Cs

9,192,631,770 Hz

e

elementary charge

1.602176634 × 10⁻¹⁹ C

ε₀

electric constant,
permitivitty of free space,
vacuum permitivitty

8.8541878188 × 10⁻¹² C²/N m²

μ₀

magnetic constant,
permeability of free space,
vacuum permeability

1.25663706127 × 10⁻⁶ T m/A

N_A

Avogadro constant

6.02214076 × 10²³ 1/mol

k

Boltzmann constant

1.380649 × 10⁻²³ J/K

R = N_Ak

gas constant

8.314462618 J/mol K

σ =	2π⁵k⁴
	15h³c²

Stefan-Boltzmann constant

5.670374419 × 10⁻⁸ W/m²K⁴

b, b′

Wien displacement constant

2897.771955 μm K
58.78925757 GHz/K

m_u

atomic mass constant

1.66053906892 × 10⁻²⁷ kg
931.49410372 MeV/c²1 u

m_e

electron mass

9.1093837139 × 10⁻³¹ kg
0.51099895069 MeV/c²5.485799090441 × 10⁻⁴ u

m_p

proton mass

1.67262192595 × 10⁻²⁷ kg
938.27208943 MeV/c²1.0072764665789 u

m_n

neutron mass

1.67492750056 × 10⁻²⁷ kg
939.56542194 MeV/c²1.00866491606 u

K_cd

luminous efficacy

683 lm/W

H₀

hubble constant*

69.3 km/s/Mpc
2.25 × 10⁻¹⁸ 1/s