Constants

This page lists various constants used in physics and some useful conversions.

Physical constants

The number in brackets represents the uncertainty in the constant, so that $6.626070040(81)\times 10^{-34}$ has an uncertainty of $0.00000000081\times 10^{-34}$ .

Name	Symbol	Value	Meaning	Used in	Exact
Planck's constant	$h$	$6.626070040(81)\times 10^{-34}\,\mathrm {J} \,\mathrm {s}$	It relates the frequency of a photon to its energy	Quantum mechanics	Inexact^[1]
Speed of light	$c$	$299,792,458\,\mathrm {m} \,\mathrm {s^{-1}}$	This is the speed of light in a vacuum	Most of physics, such as optics and relativity	Exact^[2]
Permittivity of free space	$\epsilon _{0}$	$8.854187817...\times 10^{-12}\,\mathrm {F} \,\mathrm {m^{-1}}$	Related to the strength of an electric field produced by a charge	Electromagnetism	Exact^[3]
Permeability of free space	$\mu _{0}$	$4\pi \times 10^{-7}\,\mathrm {H} \,\mathrm {m^{-1}}$	Related to the strength of [[magnetic field]s produced by a current	Electromagnetism	Exact^[4]
Elementary charge	$e$	$1.6021766208(98)\times 10^{-19}\,\mathrm {C}$	The magnitude of the electric charge on an electron	Determines the strength of electric and magnetic fields produced by protons, electrons etc	Inexact^[5]
Avogadro's number	$N_{A}$	$6.022140857(74)\times 10^{23}\,\mathrm {mol^{-1}}$	The number of constituents in 1 mole of something	Chemistry, statistical mechanics, thermodynamics	Inexact^[6]
Ideal gas constant	$R$	$8.3144598(48)\,\mathrm {J} \,\mathrm {mol^{-1}} \,\mathrm {K^{-1}}$	Relates the pressure, volume, temperature and number of moles of an ideal gas	Thermodynamics	Inexact^[7]
Faraday Constant	$F$	$96485\mathrm {C} \,\mathrm {mol^{-1}}$	The electric charge on one mole of electrons (Avogadro's number times elementary charge)	Chemistry, physics	Inexact^[8]
Gravitational constant	$G$	$6.67408(31)\times 10^{-11}\,\mathrm {N} \,\mathrm {m^{2}} \,\mathrm {kg^{-2}}$	Constant related to the strength of Newtonian gravity	Newtonian gravity	Inexact^[9]
Boltzmann constant	$k$	$1.38064852(79)\times 10^{-23}\,\mathrm {J} \,\mathrm {K^{-1}}$	Thermodynamics		Inexact^[10]
Reduced Planck's constant	$\hbar$	$1.054571800(13)\times 10^{-34}\,\mathrm {J} \,\mathrm {s}$	Quantum mechanics	It is Planck's constant divided by $2\pi$ .	Inexact^[11]
Wien displacement constant	$b$	$2.8977729(17)\times 10^{-3}\,\mathrm {m} \,\mathrm {K}$	Relates the temperature of a black body to the peak in its spectrum		Inexact^[12]
Standard acceleration due to gravity	$g$	$9.80665\,\mathrm {m} \,\mathrm {s^{-2}}$	This is the acceleration of any object near to the earth's surface when gravity is the only force acting (ie, no air resistance).	Mechanics	Exact^[13]
Proton mass	$m_{p}$	$1.672621898(21)\times 10^{-27}\,\mathrm {kg}$	Rest mass of a proton		Inexact^[14]
Neutron mass	$m_{n}$	$1.674927471(21)\times 10^{-27}\,\mathrm {kg}$	Rest mass of a neutron		Inexact^[15]
Electron mass	$m_{e}$	$9.10938356(11)\times 10^{-31}\,\mathrm {kg}$	Rest mass of an electron		Inexact^[16]