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PSI vs. PSIG — What's the Difference?

Edited by Tayyaba Rehman — By Fiza Rafique — Published on January 7, 2024
PSI measures absolute pressure, while PSIG indicates pressure above atmospheric pressure.
PSI vs. PSIG — What's the Difference?

Difference Between PSI and PSIG


Key Differences

PSI stands for pounds per square inch, a unit of pressure in the imperial system. PSIG, which stands for pounds per square inch gauge, differs in that it references pressure relative to atmospheric pressure.
In the context of PSI, the measurement includes atmospheric pressure, which is about 14.7 psi at sea level. PSIG, on the other hand, subtracts this atmospheric pressure, providing a reading of only the pressure exerted beyond the ambient air pressure.
PSI is a broader term often used in scientific and engineering contexts. PSIG, however, is more specific and is typically used in applications like tire pressure, where only the pressure above atmospheric level is relevant.
When measuring with PSI, one could get a reading above 14.7 at sea level even in an unpressurized container due to atmospheric pressure. With PSIG, such a container would show a reading of zero, emphasizing the distinction between absolute and gauge pressures.

Comparison Chart


Pounds per Square Inch
Pounds per Square Inch Gauge

Reference Point

Absolute pressure
Pressure above atmospheric

Atmospheric Influence

Includes atmospheric pressure
Excludes atmospheric pressure


General pressure measurement
Pressure in closed systems

Sea Level Reading

About 14.7 psi at sea level
Zero at sea level

Compare with Definitions


Represents the force applied over a square inch.
The hydraulic press exerts a force of 2,000 PSI.


Important in applications like tire pressure.
Inflate the tire to 32 PSIG.


A unit of pressure in the imperial system.
The pressure in the tank is 50 PSI.


Common in engineering and mechanical contexts.
The compressor's output is 120 PSIG.


Used to measure pressure in various applications.
The car's tire pressure should be 35 PSI.


Measures pressure relative to atmospheric pressure.
The pressure gauge reads 30 PSIG.


Also used in scientific calculations involving pressure.
The experiment requires a constant pressure of 10 PSI.


Used where only excess pressure matters.
For this process, maintain the pressure at 5 PSIG.


The 23rd letter of the Greek alphabet. See Table at alphabet.


Helps distinguish between absolute and gauge pressure.
The valve regulates the system to 20 PSIG.


Parapsychological phenomena or abilities considered as a group.


(countable) The twenty-third letter of Classical and Modern Greek and the twenty-fifth letter of Old and Ancient Greek.


A form of psychic energy.


A unit of pressure


The 23rd letter of the Greek alphabet


A standard unit for pressure in many industries.
The boiler operates at 150 PSI.

Common Curiosities

Is PSI the same as PSIG?

No, PSI measures absolute pressure, while PSIG measures pressure above atmospheric pressure.

What is the meaning of PSIG?

PSIG means pounds per square inch gauge.

Can PSI and PSIG have the same numerical value?

Yes, in a pressurized system, the numerical values can be the same if atmospheric pressure is not a factor.

Does atmospheric pressure affect PSIG readings?

No, atmospheric pressure is subtracted in PSIG readings.

What does PSI stand for?

PSI stands for pounds per square inch.

How is PSI used in everyday life?

PSI is commonly used to measure tire pressure, air pressure in tanks, and water pressure in pipes.

What tools measure PSI?

Pressure gauges, manometers, and sensors can measure PSI.

Is PSI used globally?

PSI is widely used, but some countries prefer the metric system (Pascals).

Where is PSIG typically used?

PSIG is often used in systems where only the pressure above atmospheric pressure is relevant, like in compressed air systems.

Does atmospheric pressure affect PSI readings?

Yes, atmospheric pressure is included in PSI readings.

What industries commonly use PSIG?

Industries like automotive, HVAC, and manufacturing commonly use PSIG.

How do you convert PSI to PSIG?

Subtract atmospheric pressure from the PSI reading to get PSIG.

Can PSIG ever be negative?

Yes, PSIG can be negative if the pressure is below atmospheric pressure.

Are PSI and PSIG used in science?

Yes, both units are used in various scientific contexts for pressure measurements.

Which is more common, PSI or PSIG?

PSI is more common in general usage, but PSIG is prevalent in specific applications like compressed systems.

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Author Spotlight

Written by
Fiza Rafique
Fiza Rafique is a skilled content writer at, where she meticulously refines and enhances written pieces. Drawing from her vast editorial expertise, Fiza ensures clarity, accuracy, and precision in every article. Passionate about language, she continually seeks to elevate the quality of content for readers worldwide.
Tayyaba Rehman is a distinguished writer, currently serving as a primary contributor to As a researcher in semantics and etymology, Tayyaba's passion for the complexity of languages and their distinctions has found a perfect home on the platform. Tayyaba delves into the intricacies of language, distinguishing between commonly confused words and phrases, thereby providing clarity for readers worldwide.

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