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Relative-, Absolut-, Differential pressure, Vacuum

Always different pressure units ...

Pa, bar, PSI, Inch-WS and more? We help you to convert.

You can find in ínternet enough helping tools and converting possibilities. Also various, which you can not really use. We have summarised for you, units related to our pressure sensors and switches.

Following value factors you can take for calculation and to get overview (more accurate with our Converter).

pressure unit (valuation)-Factor
=============== ===============
mbar = hPa 100 Pa
bar = 1000 mbar 100 kPa bzw. 0,1 MPa
PSI 70 hPa
Inch WS / Inch H2O 2,5 hPa
mWS / m H2O 100 hPa
mmWS / mm H2O 0,1 hPa = 10 Pa
mmHg bzw. Torr 1,33 hPa = 133 Pa

Absolute pressure, Relative pressure, Differential pressure, Vacuum

Absolute pressure 

  • In space is no pressure existant, but vacuum. Coming into the earth's atmosphere, pressure is increasing continuously and will be on sea level 1013,25 hPa at normal condition. The barometric or ambient pressure is a value of absolut pressure (p,abs.) ... related to vacuum.
  • Absolute pressure sensor has only one pressure port (tube or hole)

Relative pressure

  • The relative pressure is a relative relation between two pressures, whereat one pressure is always the actual atmospheric pressure (barometric or ambient pressure).   Pressure (p,rel.) ... related to ambient pressure
  • A relative pressure sensor has normally one pressure port (if you use a differential pressure sensor, one port has to be kept open to ambient).


  • Vacuum can be named as negative pressure, too. Reference point is here also the actual atmospheric pressure. In a container you have vacuum, if this pressure inside is lower than the ambient pressure. The maximal possible vacuum is according to amount alike the ambient pressure. If you have a barometric pressure of 900 hPa, max. vacuum can be -900 hPa
  • A vacuum sensor is in principle like a relative pressure sensor, not measuring pressure, but negative pressure (vacuum).

Differnetial pressure

  • Is the pressure difference between two pressures. Popular application is measurement of flow speed with aid of a blind.
  • A differential pressure sensor has 2 pressure ports. The pressure difference can have positive or negative value, pending on reference point, p1 or p2.

Familiar pressure units

According to branch, the use of "own" or to be more accurate "familiar" pressure units is standard.

To make conversion or value calculation more easy, please find some smal tools for conversion.

The correct pressure unit is, by the way, since long time Pascal (Pa).

Pascal is derived SI unit from pressure. Named after Blaise Pascal. Defined as 

1 Pa = 1 kg/(m·s²) = 1 N/m²

One Pascal is the pressure, which a force of one Newton is exerting on an area of one square meter.

Output in relation to pressure

The signal conditioning provides the wished output. On request you can have

  • mV
  • Volt
  • mA
  • Digital output