By now, you should’ve heard of the acronym PSI, pounds per square inch, which is one of the most common units of measurement for pressure. PSI is used across all industries and applications to describe the amount of force is being exerted by something.

And so, that brings us to the different types of measurements, PSI, PSIA, and PSIG. This article will provide you with all the relevant information about them and their differences.

Table of Contents

Compressed Air Pressure Measurement

PSI is an indication of the maximum pressure an air compressor can produce, and in conjunction with CFM, cubic feet per minute, is one of the key measurements to understanding the performance of an air compressor. Especially when looking to purchase a new compressor, these two values together are some of the most important considerations.

It’s important to understand that the altitude and geographic location of your compressor affect pressure measurements, and so there are 3 different ways to look at PSI:

  • PSI
  • PSIA
  • PSIG

Temperature can affect the air pressure measurements as you may know from checking your car tires in the morning on cold and warm days. Cold molecules move around more slowly and decrease the force they exert resulting in a decreased PSIG. On the contrary, if the temperature increases, molecules will move around more, and pressure will increase as a result. It’s estimated that around 1 PSIG is lost for every 10 degrees of temperature.

In terms of altitude, the greater the altitude the lower the atmospheric pressure. Though it’s not a lot, estimated at around .5 PSIG per 1000 feet, it’s still something to be aware of! But the important consideration is that as altitude changes, so does the temperature. So, a compressor at a higher elevation in a colder temperature will have to work harder to operate at the same pressure as a compressor at sea level in a warmer temperature.  


What is PSI?

PSI stands for the pounds per square inch and is a measure of the force delivered by air compressors. For instance, a compressor could be rated 120 PSI which means it can deliver 120 pounds of pressure per square inch.

What is PSIA?

PSIA stands for the pounds per square inch absolute. Which is sometimes referred to as the total pressure, PSIA is the pressure relative to zero, or a perfect vacuum.

What is PSIG?

The term PSIG stands for pounds per square inch gauge and is used for PSI in relation to atmospheric pressure. The ambient pressure at sea level is 14.696 PSIA, but ambient PSIG is always taken at 0.

How to Calculate PSIA & PSIG

An important fact to remember is that PSIG is always lower than PSIA. The formulas that are used to describe their relationship are:

PSIA = PSIG + 1 atm

PSIG = PSIA – 1 atm


PSIA = pounds per square inch absolute

PSIG = pounds per square inch gauge

Atm = Atmospheric pressure

It’s extremely each to convert between the two or calculate either PSIA or PSIG if you know the atmospheric pressure value for your location and add it into the formula. If you don’t know the atmospheric pressure value for your area, you can use the standard atmospheric value of pressure at sea level 14.7 (14.696) PSI.


How do I convert PSIG to PSIA?

To convert PSIG to PSIA, you must take the PSIG value and add 1 atmospheric pressure. This should be the atmospheric pressure value of your location, but if you cannot find out what it is you can use 14.7 PSI which is standard atmospheric pressure at sea level.

What does 14.7 PSIA represent?

14.7 PSIA, or 14.696 PSIA to be more precise, represents the value of standard atmospheric pressure at sea level.

What does PSIA stand for?

PSIA stands for the pounds per square inch absolute. It’s a measurable pressure in relation to a perfect vacuum.

If you have any questions regarding PSIA vs PSIG vs PSI, please leave a comment below, with a photo if applicable, so that someone can help you!