PSIG vs PSI: What's their Difference

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Different units of pressure are used for measurements in various industries. A varied scale helps in measuring minute variations and this is one of the reasons why different units are used for the measurement of pressure. One of the places where measuring pressure is common is pipeline systems. When it comes to pipelines and valves, pressure is always a constant factor that needs to be understood.

Pressure gauges installed in a submarine
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When it comes to piping and related sectors, the common units used are PSI, PSIG, and PSIA. PSI stands for Pounds per Square Inch, PSIG for Pounds per Square Inch Gauge, and PSIA for PSI Absolute. Many people get confused while considering PSIG vs PSI because these two units sound similar. 

But these units are not similar – there are a lot of differences between them and caution must be practiced while measuring pressure using these units.

We’ll take a look at the meaning of these units and the differences between them.

What is PSI?

Pressure can be defined as the force exerted on an object by the area over which the pressure is being applied. There are many standard units for measuring and expressing pressure, and one of the most common ones used across the US is the unit PSI.

PSI stands for Pound per Square Inch, and it is not the SI unit of pressure. The SI unit for pressure is Pascal and it can be understood as the pressure experienced in an area of 1 square meter when a force of 1 Newton is applied. PSI, on the other hand, is expressed through pounds of force per square inch area.

A Pressure Gauge
Source: Pexels

PSI is a unit often used for measuring pressure in industrial applications. Instruments like pressure gauges and sensors usually display pressure values in terms of PSI.

1 PSI is equal to:

  • 0.068046 atmospheres
  • 0.0689476 Bar
  • 6894.76 Pascals

When it comes to industrial valves and measuring pressure, PSI is the standard unit. In a valve or a pipeline, the pressure of the fluid inside the pipeline is measured. In this context, PSI will be the pressure created by one pound force of fluid per square inch of pipe.

Often, PSI and PSIG are confused and used in the wrong places. PSIG vs PSI can be easily understood when the meaning of PSIG is made clear.

Where is it Used?

While PSI is commonly used for measuring in a wide range of applications, it can also be primarily used for measuring pneumatic and hydraulic pressure. One can find applications for this unit also in water management systems, fire safety valving, and pipelining. 

It is widely applied for technical purposes and measurements in various places including measuring tire pressure, test and management activities, and wastewater management activities. This unit is also employed in the valve manufacturing industry.

What is PSIG?

PSIG is PSI gauge pressure, and this pressure is the value that expresses relative pressure. Gauge pressure is expressed in pounds per square inch gauge – it is the pressure value relative to ambient or atmospheric pressure. While calculating PSIG, the local atmospheric pressure is not calculated as a part of the value. 

In simple terms, PSIG can be understood as the pressure difference between the pressure in a pipe and the atmospheric pressure. It is measured using a gauge or a similar instrument. PSIG is measured when the pressure inside a valve or a pipeline is more than atmospheric pressure. 

One of the most crucial points to note about PSIG is that it is a measurement of only gauge pressure. Gauge pressure in general refers to the measurement of pressure relative to atmospheric pressure. PSIG is measured in PSI units.

PSIG can also be expressed in terms of PSIA, or Absolute PSIA. Absolute pressure or total pressure is the value of pressure in PSI in addition to atmospheric pressure. PSIG is always lower than absolute pressure.

PSIG = PSIA – 1 atm (atm = atmospheric pressure)

Pressure measurements in a system
Source: Energy Education

Comparing PSI versus PSIG can be a bit confusing, as both the units are somewhat similar. But when it comes to practical applications, it is easy to understand the difference between them. Without knowing the similarities and differences between these units, it is difficult to understand the working of instruments that measure pressure in these units.

Where is it Used?

PSIG is most commonly employed in transport and industrial valve industries. This is because the unit is easier when it comes to measuring tire and valve pressure, coolant pressure, etc… As PSIG refers to the pressure inside compared to the atmospheric pressure outside, the PSIG value of an emptied tire would be -14.7 PSI.

This measurement is also used while recording pressure in HVAC and refrigeration systems. As the gauge pressure often ignores local pressure factors, it is employed in situations like these.

A man checking the pressure in a car tire
Source: Pexels

What is PSIG vs PSI – The Differences and their Meanings

When the debate of PSIG vs PSI arises, it is important to consider the standard definitions of the two units and how they differ from one another in the application. Here are some important differences between PSIG and PSI.

It is a non-SI unit for measuring pressure.It is a measure of gauge pressure.
PSI can be understood as the amount of pressure exerted on an object with a surface area of one square when a force of one pound is applied.PSIG is the measurement of pressure relative to atmospheric pressure.
PSI is in itself a unit.PSIG is measured in terms of PSI.It
It is widely used in the valve and pipeline industry, water management industry, and fire safety valving.It is commonly applied in the transport industry, especially when it comes to tire pressure.
PSI can be converted to other units like Pascal and Bar.PSIG is relative pressure, so it uses units like PSI and Pascal for measurement.
PSI is measured relative to vacuum.PSIG is measured relative to atmospheric pressure.

PSIG vs PSI and Valves

Valves have two main types of pressure ratings: body pressure ratings and close-off pressure. The Body Pressure Rating refers to the amount of pressure that a valve’s main body and stem can withstand without resulting in leakage. As for the close-off pressure, it is the utmost pressure that a valve can hold across a ball or disc, depending upon the type of valve.

Valves with pressure gauges
Source: Pixabay

Both of these ratings are measured in PSI. For example, WOG (water, oil, gas) is one of the common ratings for industrial valves, and a rating of 500 WOG will mean that the valve can withstand a body pressure of 500 PSI. 

The pressure ratings of industrial valves are determined by several standards like ISO and ASME. The ASME standard B16.34 defines the pressure and temperature ratings suitable for valves made of different materials.


Be it any valve manufacturing or any other industry, it is important to know about PSIG vs PSI and how these units are used in measuring pressure. By understanding the basic differences between these two units, one can understand more about how these pressure ratings are applied for industrial valves. Any industrial valve manufacturer should produce valves that adhere to valve ratings and standards.

If you are looking for a quality valve manufacturer, DomBor is the right choice for you. With over ten years of experience in this field, DomBor specializes in manufacturing a wide range of industrial valves. We also offer customization services for all our clients – contact us today and get your custom valves designed and manufactured by us.