Mean Free Path Calculator

Find the average distance a gas molecule travels between collisions.

Mean free path 0

Formula: λ = k·T ÷ (√2·π·d²·P)

Step-by-step with your numbers:

1. Values used:

2. Temperature = 300 K

3. Pressure = 101,325 Pa

4. Molecule diameter = 370 pm

6. Mean free path = 0

Did we solve your problem today?

The mean free path is how far a molecule typically travels before hitting another.

The math behind it

λ = k·T ÷ (√2·π·d²·P). Lower pressure means longer free paths.

Air at 300 K, 1 atm, d 370 pm → about 68 nm.

Why does it matter for vacuum?

At low pressure the path can exceed chamber size, changing the flow regime.