Understanding and converting pressure units: PSI, PSIA and PSIG to bar

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!

What is PSI?

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.

1 PSI is:

  • 0.068046 atmospheres

  • 0.0689476 Bar

  • 6894.76 Pascals

  • 51.7149 Torr

  • 2.03602 inHg

  • 27.7076 inches water column

Pressure conversion: PSI to bar

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.

Converting PSI to bar – examples

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

What does the PSIA unit mean?

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.

PSIA unit – applications

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.

What is PSIG unit?

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.

PSIA and PSIG – air pressure measurements

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.

How do you convert PSIG to bar?

1 PSIG unit is equal to 1.082198 bar.