Knudsen Number Calculator
Find the Knudsen number to classify a flow regime.
The Knudsen number tells whether a gas behaves as a continuous fluid or as individual molecules.
The math behind it
Kn = λ ÷ L. Kn < 0.01 is continuum flow; Kn > 10 is free molecular flow.
Worked example
λ 70 nm, L 1 mm → Kn ≈ 7 × 10⁻⁵ (continuum).
FAQ
When does continuum break down?
At low pressure or tiny scales (MEMS, vacuum), where Kn becomes large.