Boltzmann constant

physical constant relating energy at the individual particle level with temperature
For the constant pertaining to energy of black body radiation see Stefan–Boltzmann constant
Values of k Units
1.380649×10−23 JK−1
8.617333262×10−5 eV K−1
1.380649×10−16 erg K−1

The Boltzmann constant (k or kB) is a physical constant. It is defined to be 1.380649×10−23 J/K.[1] It relates the average kinetic energy of a particle in a gas with the temperature of the gas. It is the gas constant R divided by the Avogadro constant NA:

The Boltzmann constant has SI units of J⋅K−1 (also written J/K), the same as entropy. It is named after the Austrian physicist Ludwig Boltzmann.


  1. SI Brochure: The International System of Units (SI) (PDF) (Ninth ed.), Bureau International des Poids et Mesures, 2019, p. 129, retrieved 2020-01-18 CS1 maint: discouraged parameter (link)