Thread: Difference between psia, psig and psi

hello
I have a big problem with pressure's units

I know that P (psig) = (P + 14.7) psia

But my problem with psi

as an example, 20 psi = ?? in psia or psig ??

Originally Posted by BayernMunich

hello
I have a big problem with pressure's units

I know that P (psig) = (P + 14.7) psia

But my problem with psi

as an example, 20 psi = ?? in psia or psig ??

PSI (lbs/in^2) is a just a unit of pressure. In a problem situation, one has to pay attention if the PSI given is an absolute or gauge pressure reading.

PSIA is measured in units of PSI and the reference for zero PSIA is a perfect vacuum.

A pressure gauge reads the pressure difference between its location and the ambient pressure. PSIG is gauge pressure, also measured in units of PSI. The zero for PSIG is ambient or atmospheric pressure at sea level, (on Earth, approx 14.7 PSI), that is why PSIG - 14.7 = PSIA