Physical Constants

Glenn Elert

Physical Constants

Reference

Physical constants (exact, computed, measured) Sources: exact, BIPM; measured, NIST and/or PDG, *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

6.626 070 15 × 10⁻³⁴ J s
4.135 667 696 × 10⁻¹⁵ eV s

hc

h c

1.986 445 857 × 10⁻²⁵ J m
1239.841 984 eV nm

ℏ =	h
	2π

h bar,
reduced Planck constant,
Dirac constant

1.054 571 817 × 10⁻³⁴ J s
6.582 119 569 × 10⁻¹⁶ eV s

f_Cs

hyperfine transition of ¹³³Cs

9,192,631,770 Hz

e

elementary charge

1.602 176 634 × 10⁻¹⁹ C

ε₀

electric constant,
permitivitty of free space,
vacuum permitivitty

8.854 187 818 8 × 10⁻¹² C²/N m²

μ₀

magnetic constant,
permeability of free space,
vacuum permeability

1.256 637 061 27 × 10⁻⁶ T m/A

N_A

Avogadro constant

6.022 140 76 × 10²³ 1/mol

k

Boltzmann constant

1.380 649 × 10⁻²³ J/K

R = N_Ak

molar gas constant

8.314 462 618 J/mol K

σ =	2π⁵k⁴
	15h³c²

Stefan-Boltzmann constant

5.670 374 419 × 10⁻⁸ W/m²K⁴

b, b′

Wien displacement constant

2897.771 955 μm K
58.789 257 57 GHz/K

m_u

atomic mass constant
atomic mass unit
unified atomic mass unit

1.660 539 068 92 × 10⁻²⁷ kg
931.494 103 72 MeV/c²
1 u

m_e

electron mass

9.109 383 701 5 × 10⁻³¹ kg
0.510 998 950 00 MeV/c²5.485 799 090 65 × 10⁻⁴ u

m_p

proton mass

1.672 621 923 69 × 10⁻²⁷ kg
938.272 088 16 MeV/c²1.007 276 466 621 u

m_n

neutron mass

1.674 927 498 0 × 10⁻²⁷ kg
939.565 420 5 MeV/c²1.008 664 916 0 u

K_cd

luminous efficacy

683 lm/W

H₀

hubble constant*

69.3 km/s/Mpc
2.25 × 10⁻¹⁸ 1/s