# 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*