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Table of Mean Free Path at pressure stages
Vacuum Range Pressure (mmHg or Torr) Pressure (psi) Molecules /cm3 Mean Free Path
Ambient pressure 759.8 14.69 2.7 x 1025 68 nm
Low Vacuum 225-7.501x10-1 4.35 - 0.0145 1025 - 1022 0.1 - 100 μm
Medium Vacuum 7.501x10-1 - 7.501x10-4 0.0145 - 0.00001 1022 - 1019 0.1 - 100 mm
High Vacuum 7.501x10-4 - 7.501x10-8 0.00001 - 1.450 x 10-9 1019 - 1015 10 cm - 1 km
Ultra-High Vacuum 7.501x10-8 - 7.501x10-13 1.450 x 10-9 - 1.450 x 10-14 1015 - 1010 1 km - 105 km
Extra-High Vacuum < 7.501x10-13 1.45 x 10-14 <1010 > 105 km

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