Boltzmann constant | |
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![]() Ludwig Boltzmann, the constant's namesake | |
Symbol: | kB, k |
Value in joules per kelvin | 1.380649×10−23 J⋅K−1[1] |
Value in electronvolts per kelvin | 8.617333262×10−5 eV.K-1[1] |
The Boltzmann constant (kB or k) is the proportionality factor that relates the average relative thermal energy of particles in a gas with the thermodynamic temperature of the gas.[2] It occurs in the definitions of the kelvin (K) and the gas constant, and in Planck's law of black-body radiation and Boltzmann's entropy formula, and is used in calculating thermal noise in resistors. The Boltzmann constant has dimensions of energy divided by temperature, the same as entropy and heat capacity. It is named after the Austrian scientist Ludwig Boltzmann.
As part of the 2019 redefinition of SI base units, the Boltzmann constant is one of the seven "defining constants" that have been given exact definitions. They are used in various combinations to define the seven SI base units. The Boltzmann constant is defined to be exactly 1.380649×10−23 joules per kelvin.[1]
SI2019
was invoked but never defined (see the help page).