Mean Free Path Calculator
Enter gas temperature, pressure, and molecular diameter to calculate the average distance a particle travels between collisions.
Input Parameters
Enter gas conditions to calculate the mean free path.
Room temperature ≈ 300 K, absolute zero = 0 K
Mean Free Path (λ)
Enter values and click Calculate
Meters (m)
Micrometers (µm)
Nanometers (nm)
Angstroms (Å)
Derived Quantities
Results appear after calculation
Number density (n)
Collision frequency (z)
Mean speed (v̄)
Knudsen regime
Formula Used
λ = kT / (√2 · π · d² · P)
- λ
- mean free path
- k
- Boltzmann constant (1.380649 × 10⁻²³ J/K)
- T
- temperature (K)
- d
- molecular diameter (m)
- P
- pressure (Pa)
Summary
Enter gas temperature, pressure, and molecular diameter to calculate the average distance a particle travels between collisions.
How it works
- Enter the gas temperature in Kelvin (e.g. 300 K for room temperature).
- Enter the gas pressure in Pascals (e.g. 101325 Pa for 1 atmosphere).
- Enter the effective molecular diameter in nanometers (e.g. 0.372 nm for nitrogen).
- Click Calculate — the tool applies the kinetic theory formula λ = kT / (√2 · π · d² · P).
- Results show the mean free path in meters, micrometers, and nanometers.
Use cases
- Estimate the mean free path of air molecules at standard conditions.
- Understand vacuum system design by calculating MFP at different pressures.
- Study astrophysical gas clouds and interstellar medium particle behavior.
- Compare MFP across different gases by varying molecular diameter.
- Explore how pressure changes (e.g. high altitude) affect collision frequency.
- Support kinetic theory and thermodynamics coursework calculations.
Frequently Asked Questions
Last updated: 2026-07-22 ·
Reviewed by Nham Vu