Vacuum
Vacuum is defined as air pressure below atmospheric pressure.
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
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 <
Related Topics

Gases and Compressed Air
Air, LNG, LPG and other common gas properties, pipeline capacities, sizing of relief valves.
Related Documents

Atmospheric Pressure vs. Elevation above Sea Level
Elevation above sea level  in feet and meter  with barometric and atmospheric pressure  inches mercury, psia, kg/cm^{2} and kPa. 
Vacuum  Air Expansion Ratio
Convert vacuum air volume to standard air volume 
Vacuum  Evacuation Time
Vacuum pumps  calculate flow rate and required evacuation time. 
Vacuum  Flow Measurement
Measure air volume flow in vacuum. 
Vacuum  Pressure Units Converter
Converting between vacuum units like % vacuum  mm Mercury  psi  torr  micron  kPa. 
Vacuum Pipes  Flow Velocities
Air velocity diagrams for vacuum pipe lines. 
Vacuum Pipes  Pressure Loss vs. Air Flow
Calculate pressure drops in vacuum pipe lines. 
Vacuum Pumps  Exhaust Pipe Capacities
Capacities of vacuum pump exhaust pipes. 
Water  Boiling Points at Vacuum Pressure
Online calculator, figures and tables giving the boiling temperatures of water in varying vacuum, SI and Imperial units.