How do you convert PSIG to PSIA?

• A. Subtract 14.7
• B. Add 14.7
• C. Multiply by 2
• D. Divide by 2

Answer: (B)

Gauge pressure (PSIG) is how much pressure sits above the surrounding atmosphere, while absolute pressure (PSIA) is the pressure relative to a vacuum. To convert from PSIG to PSIA you add the atmospheric pressure, because you’re accounting for the air already pushing on you. At sea level, that atmospheric pressure is about 14.7 psi, so PSIA = PSIG + 14.7 psi. For example, 10 psig becomes 24.7 psia. If there’s zero gauge pressure, the absolute pressure is still 14.7 psia due to the air around us.