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 $\text{[math]}$ has an uncertainty of $\text{[math]}$ .

Name	Symbol	Value	Meaning	Used in	Exact
Planck's constant	$\text{[math]}$	$\text{[math]}$ J s	It relates the frequency of a photon to its energy	Quantum mechanics	Inexact^[1]
Speed of light	$\text{[math]}$	299,792,458 m 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	$\text{[math]}$	$\text{[math]}$ F m^-1	Related to the strength of an electric field produced by a charge	Electromagnetism	Exact^[3]
Permeability of free space	$\text{[math]}$	$\text{[math]}$	Related to the strength of [[magnetic field]s produced by a current	Electromagnetism	Exact^[4]
Elementary charge	$\text{[math]}$	$\text{[math]}$ 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	$\text{[math]}$	$\text{[math]}$ mol^-1	The number of constituents in 1 mole of something	Chemistry, statistical mechanics, thermodynamics	Inexact^[6]
Ideal gas constant	$\text{[math]}$	$\text{[math]}$ J mol^-1 K^-1	Relates the pressure, volume, temperature and number of moles of an ideal gas	Thermodynamics	Inexact^[7]