What This Calculator Does
The mean free path is the average distance a gas molecule travels before colliding with another molecule. It’s a fundamental quantity in the kinetic theory of gases, used in fields from vacuum technology to atmospheric science.
The Formula
Mean free path is calculated as λ = (kẙT) / (√2 × π × d² × P), where kẙ is Boltzmann’s constant (1.380649×10⁻²³ J/K), T is absolute temperature in Kelvin, d is the effective molecular diameter, and P is pressure in pascals.
Note: The default molecular diameter (about 370 picometers) approximates air molecules. Mean free path increases at low pressure and high temperature, which is why it becomes significant in vacuum systems.
Last reviewed August 2026