PSIG to PSIA Converter

How to Convert PSIG to PSIA

PSIG (pounds per square inch gauge) and PSIA (pounds per square inch absolute) are two ways to express pressure in the same unit system. PSIG measures pressure relative to the local atmosphere, which is how most tire gauges, compressed air systems, and industrial pressure instruments display readings. PSIA measures total pressure from a perfect vacuum, which is required for thermodynamic calculations, gas law problems, and engineering design.

The key difference is atmospheric pressure. At sea level, standard atmospheric pressure is approximately 14.696 psi. To convert gauge pressure to absolute pressure, you add this atmospheric offset.

For related pressure conversions, try our MPa to PSIG Converter, Pressure Converter, or PSI to ATM Converter.

The Conversion Formula

To convert PSIG to PSIA:

$$\text{PSIA} = \text{PSIG} + 14.696$$

To convert PSIA to PSIG:

$$\text{PSIG} = \text{PSIA} - 14.696$$

For example, a tire gauge reading of 30 psig equals 44.696 psia (30 + 14.696). Atmospheric pressure at sea level equals 14.696 psia, which is 0 psig on a gauge.

PSIG vs PSIA: When to Use Each

Use PSIG when reading everyday pressure gauges. A car tire at 32 psig means the tire pressure is 32 psi above the surrounding air. Use PSIA when working with absolute pressure values, such as calculating gas density, designing vacuum systems, or comparing pressures across different altitudes where atmospheric pressure changes.

Negative PSIG values indicate vacuum (pressure below atmosphere). A reading of -5 psig equals 9.696 psia, meaning the pressure is 5 psi below atmospheric.

Quick Reference Table

• 0 psig = 14.696 psia (atmospheric pressure at sea level)
• 14.696 psig = 29.392 psia (twice atmospheric)
• 30 psig = 44.696 psia (typical car tire pressure)
• 100 psig = 114.696 psia (industrial compressed air)
• -14.696 psig = 0 psia (perfect vacuum)