PSIG (pounds per square inch gauge) measures pressure relative to atmospheric pressure. PSI (pounds per square inch) is the absolute pressure, including atmospheric pressure.
The formula to convert PSIG to PSI is:
\[ \text{PSI} = \text{PSIG} + 14.7 \]
Consider a pressure reading of 30 PSIG:
Using the formula:
\[ \text{PSI} = 30 + 14.7 = 44.7 \text{ psi} \]
This means the absolute pressure is 44.7 psi.