Definition of Vacuum

Vacuum is the term for air pressures which lie below normal atmospheric pressure. The ambient pressure is 1,013 mbar at sea level and decreases with elevation. The form of the vacuum depends on the application in vacuum technology. A relatively small vacuum, the low vacuum, is sufficient for vacuum handling. The pressure of the low vacuum ranges from 1 mbar to 1,013 mbar (ambient pressure at sea level).

Specification as relative value

In vacuum technology, the vacuum is specified as a relative value which means the vacuum is specified in relation to the ambient pressure. Such vacuum values always have a negative sign, because the ambient pressure is used as the reference point, which is defined as 0 mbar.

Specification as absolute value

In science, a vacuum is specified as an absolute value. The reference point is absolute zero, which means space void of air (e.g. outerspace). This means the vacuum value is always positive.

Vacuum/pressure conversion table

The following table shows the comparison values between absolute and relative pressure.

Absolute pressure [mbar]Relative vacuumbarN/cm2kPaatm, kp/cm2mm H2OTorr; mm Hgin Hg


Further information regarding conversion, energy consumption and atmospheric pressure can be found on the following pages:

Conversion and unit tables
Measurement units for vacuum data
Energy required for vacuum generation
The atmosphere and its effects on vacuum technology