# Difference between gauge pressure and absolute pressure measurement

Again and again, we are asked the question about the difference between an absolute pressure measurement and a gauge pressure measurement. To answer this question it can help to look at the definition of gauge pressure and absolute pressure. The difference between your two measurements is then explained relatively simply and thus also the decision of the appropriate measurement.
Definition of absolute pressure
Absolute pressure is really a pressure that is in accordance with the zero pressure in the empty, air-free space of the universe. This reference pressure is the ideal or absolute vacuum. It is denoted with the subscript ?abs?: Pabs.
Release of gauge pressure
The gauge pressure means the difference between an absolute pressure (Pabs) and the prevailing atmospheric pressure (Pamb). It is denoted with the subscript ?e?: Pe and is calculated as follows: Pe = Pabs ? Pamb.
Absolute vs gauge pressure measurement
The difference between your two measurements is relatively easily clarified: in a gauge pressure measurement, it is usually the difference from the current ambient pressure that’s measured. However, this pressure changes with the weather and the height above sea level. A complete pressure measurement measures the difference from the ideal or absolute vacuum. This is the reason this measurement is independent of environmental influences such as weather or altitude. Which Lonely is currently the right one?
In practice, the two measurements can be differentiated the following: typically, the measuring task would be to determine the gauge pressure. This is exactly why this kind of sensor is hottest. However, in case a gauge pressure sensor is used in an application where the actual measuring task would be to measure the absolute pressure, the following additional errors must be expected:
+/- 30 mbar due to changes in weather
up to 200 mbar when changing the positioning (e.g. from sea level to 2,000 m)
Depending on measuring range, these errors can be substantial (e.g. in pneumatics at a measuring selection of 1 bar) or negligible (in hydraulics at 400 bar).
Note
If you are uncertain whether your measuring task needs an absolute pressure or gauge pressure measurement, simply e mail us ? we?ll be glad to assist you.