What this calculator does
Mean free path of a gas works out average distance a gas molecule travels between collisions with other molecules. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
Formulaλ = k_BT / (√2·π·d²·P), k_B = 1.380649×10⁻²³ J/K (exact)
The inputs explained
| Field | What to enter |
|---|---|
| Temperature (K) | A number, measured in K. Starts at 293.15. |
| Pressure (Pa) | A number, measured in Pa. Starts at 101325. |
| Molecular diameter (air ≈ 3.7×10⁻¹⁰) (m) | A number, measured in m. Starts at 3.7e-10. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with temperature
Every other input is held at the calculator’s starting values while temperature varies. Select any row to load that scenario into the calculator.