The Boltzmann constant, kR, is a physical constant that relates the average kinetic energy of particles in a gas with the temperature of the gas. The constant is commonly used in the Ideal Gas Law.

If the temperature is measured in Kelvin and the energy in Joules the constant gets the following value in SI units:

kR = 1.38 × 10−23 J/K.

The value of the constant has to be adjusted to the temperature scale selected.