PSIG (gauge pressure) and PSIA (absolute pressure) differ by exactly standard atmospheric pressure — a reference-point shift, not a unit-scale conversion.
How it works
Adding standard atmospheric pressure (14.696 psi) to a gauge reading gives absolute pressure; subtracting it from an absolute reading gives gauge pressure back.
What this does not include
This does not include conversions to other pressure units like bar or pascals — for those, use this site’s full pressure converter instead. This tool specifically shifts between the gauge and absolute reference points, both in psi.
How to use this calculator
- Enter a value in either PSIG or PSIA — the other field fills in automatically.
Frequently asked questions
What’s the difference between gauge and absolute pressure?
Gauge pressure is measured relative to atmospheric pressure (so 0 psig means “same as the surrounding air”); absolute pressure is measured relative to a perfect vacuum (so 0 psia means “no pressure at all”).
Why does a tire gauge read PSIG rather than PSIA?
Because what matters for tire performance is the pressure above and beyond the atmosphere already pressing on the tire from outside — gauge pressure captures that directly.
Where is PSIA commonly required instead of PSIG?
Scientific and engineering calculations involving gas laws, where the true total pressure (including atmospheric) matters for the physics involved.
