Different pressure units are used depending on the country as well as the application. In this article, we explain by means of practical examples what the PSI, PSIA and PSIG units are and how to convert them into the commonly used in gauge pressure measurement bar. Check it out!
PSI (pounds per square inch) is a derived unit of pressure or pressure stress. It is used for industrial and technical purposes, such as tyre pressure, fuel storage and distribution or measurements in water and wastewater management, among others.
In a scientific context (e.g. in laboratories), pressure is usually measured in much smaller units called Pascals.
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The PSI unit is more common in Anglo-Saxon countries such as the United Kingdom or the United States. Therefore, you may need to convert it to the bar unit, which is more commonly used in our country.
1 unit of PSI is 0.0689476 Bar.
As an example, here is a conversion of some of the most common units of PSI to bar in industry:
5 psi to bar 0.344735 bar
30 psi to bar 2.07 bar
35 psi to bar 2.41 bar
50 psi to bar 3.45 bar
60 psi to bar 4.14 bar
100 psi to bar 6.89 bar
150 psi to bar 10.34 bar
PSIA, or absolute PSI, is a unit of absolute pressure measured against a full vacuum. The pressure in a vessel completely free of air molecules would be 0 PSIA, while the average atmospheric pressure at the earth's surface (at sea level) is approximately 14.7 PSIA.
This unit is used, among other things, in meteorology. It can also be encountered when reading values from pressure gauges on valves and equipment used in oil fields.
The PSIA unit is used to measure pressure in oilfields, among others.
The PSIG unit refers to the difference between the pressure measured by, for example, a manometer or pressure transducer in a pipe and the atmospheric pressure. This unit is often used in the transport industry.
PSIG, that stands for pounds per square inch gauge, is always lower than PSIA (pounds per square inch absolute). The formulae describing this relationship are: PSIG + 1 atm = PSIA and PSIA - 1 atm = PSIG (where atm is atmospheric pressure). To calculate PSI and PSIG or to convert between the two, use the actual atmospheric pressure value for your location if you have access to this data or assume a PSI of 14.7. This is an approximate atmospheric pressure at sea level and unless you are at high altitude or in a valley, this assumption will work.
1 PSIG unit is equal to 1.082198 bar.