# Fundamental Physical Constants

**Fundamental Physical Constants**

**Name Symbol Value**

Speed of light in vacuum *c *2.99792458 * 108 m>s

Magnitude of charge of electron *e *1.602176634 * 10-19 C

Gravitational constant *G *6.674081312 * 10-11 N # m2>kg2

Planck’s constant *h *6.62607015 * 10-34 J # s

Boltzmann constant *k *1.380649 * 10-23 J>K

Avogadro’s number *N*A 6.02214076 * 1023 molecules>mol

Gas constant *R *= *N*A*K *8.314462618c J>mol # K

Mass of electron *m*e 9.109383561112 * 10-31 kg

Mass of proton *m*p 1.6726218981212 * 10-27 kg

Mass of neutron *m*n 1.6749274711212 * 10-27 kg

Magnetic constant m0 1.25663706 * 10-6 Wb>A # m 1approximate2 _ 4p * 10-7 Wb>A # m

Electric constant P0 = 1>m0 *c*2 8.854187817 * 10-12 C2>N # m2 1approximate2

1>4pP0 8.987551787 * 109 N # m2>C2 1approximate2

**Other Useful Constants***

Mechanical equivalent of heat 4.186 J>cal 115 calorie2

Standard atmospheric pressure 1 atm 1.01325 * 105 Pa

Absolute zero 0 K -273.15 C

Electron volt 1 eV 1.60217662091982 * 10-19 J

Atomic mass unit 1 u 1.6605390401202 * 10-27 kg

Electron rest energy *m*e *c*2 0.51099894611312 MeV

Volume of ideal gas 10 C and 1 atm2 22.4139621132 liter>mol

Acceleration due to gravity (standard) *g *9.80665 m>s2

***Source:** National Institute of Standards and Technology (**https://physics.nist.gov/cuu/Constants/**). Numbers in parentheses show the uncertainty in the final digits of the main number; for example, the number 1.6454(21) means 1.6454 { 0.0021. Values shown without uncertainties are exact. The exact values of the magnitude of the charge of the electron, **Planck’s constant**, the **Boltzmann constant**, **Avogadro’s constant**, and the gas constant are from the redefinitions adopted in 2018. As consequences of these redefinitions, the values of the magnetic constant and electric constant now have fractional uncertainties of about 2 * 10-10. As of this writing it was expected that updated values of the magnetic and electric constants, as well as of all other constants with uncertainties, were to be announced in May 2019. These updated values will be available at **https://physics.nist.gov/cuu/Constants/**