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Mean Free Path of an Ideal-Gas Molecule Calculator

λ = k_B·T / (√2 · π · d² · P).

Compute the mean free path λ — the average distance an ideal-gas molecule travels between collisions — from temperature, pressure, and the kinetic-theory hard-sphere collision diameter d: λ = k_B·T / (√2 · π · d² · P). Defaults represent N₂ at 25 °C and 1 atm (d ≈ 3.7 × 10⁻¹⁰ m).

Dr. Helena Ortiz By Dr. Helena Ortiz
Published Last reviewed 1 min read

Inputs

K
Pa
pm

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

λ = k_B·T / (√2 · π · d² · P), k_B = 1.380649×10⁻²³ J/K.

In depth

Compute the mean free path λ — the average distance an ideal-gas molecule travels between collisions — from temperature, pressure, and the kinetic-theory hard-sphere collision diameter d: λ = k_B·T / (√2 · π · d² · P). Defaults represent N₂ at 25 °C and 1 atm (d ≈ 3.7 × 10⁻¹⁰ m).