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Vacuum is defined as air pressure below atmospheric pressure

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The vacuum level is the difference in pressure between atmospheric pressure and pressure in the evacuated system:

  • 0% vacuum = 760 torr = 14.7 psia = 29.92 inc mercury abs = 101.4 kPa abs
  • 50% vacuum = 380 torr = 7.3 psia = 15 inc mercury abs = 50.8 kPa abs
  • 99.9% vacuum = 1 torr = 0.01934 psia = 0.03937 inc mercury abs = 1.3 kPa abs

For perfect vacuum (100%) - the pressure is 0 torr, 0 psia or 0 Pa abs.

Vacuum versus Absolute Air Pressure

air pressure versus vacuum

Example - Vacuum

If the absolute pressure is 60 kPa the vacuum according the diagram above is approximately 40% - or approximately 450 Torr.

Vacuum Ranges

  • atmospheric pressure - 760 torr
  • low vacuum - 760 to 25 torr
  • medium vacuum - 25 to 10-3 torr
  • high vacuum - 10-3 to 10-9 torr
  • ultra high vacuum - 10-9 to 10-12 torr
  • extremely high vacuum - < 10-12 torr
  • perfect vacuum - 0 torr

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