Mean free path Mean free path in kinetic theory Mean free path in kinetic theory

| 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 |