Mean free path
Mean free path in kinetic theory
Columns: Vacuum range | Pressure in hPa (mbar) | Molecules / cm 3 | Molecules / m 3 | Mean free path
Ambient pressure | 1013 | 2.7 × 10 19 | 2.7 × 10 25 | 68 nm | Low vacuum | 300 – 1 | 10 19 – 10 16 | 10 25 – 10 22 | 0.1 – 100 μm | Medium vacuum | 1 – 10 −3 | 10 16 – 10 13 | 10 22 – 10 19 | 0.1 – 100mm | High vacuum | 10 −3 – 10 −7 | 10 13 – 10 9 | 10 19 – 10 15 | 10cm – 1km | Ultra high vacuum | 10 −7 – 10 −12 | 10 9 – 10 4 | 10 15 – 10 10 | 1km – 10 5 km | Extremely high vacuum | <10 −12 | <10 4 | <10 10 | >10 5 km