PSIG към PSIA

Pressure measurement is critical across industrial automation, HVAC/R engineering, aerospace, pneumatics, and chemical processing. Understanding the exact distinction between gauge pressure (PSIG) and absolute pressure (PSIA) prevents catastrophic equipment miscalibrations, piping failures, and safety hazards.

1. Understanding PSIG vs PSIA

PSIG (Pounds per Square Inch Gauge) measures pressure relative to ambient atmospheric pressure. A standard pressure gauge open to room air reads 0 PSIG because atmospheric air presses equally on the inside and outside of the gauge sensor diaphragm.

PSIA (Pounds per Square Inch Absolute) measures pressure relative to a perfect, complete vacuum (0 PSIA). Because Earth's atmosphere exerts weight, air at sea level pushes down with approximately 14.6959 psi (14.7 psi). Therefore, a vessel at 0 PSIG contains 14.7 PSIA of absolute pressure.

2. The Conversion Formula

The mathematical relationship is direct and linear:

PSIA = PSIG + Local Atmospheric Pressure (P_atm)

Conversely, to convert PSIA back to PSIG:

PSIG = PSIA - Local Atmospheric Pressure (P_atm)

3. Impact of Altitude & Atmospheric Pressure Variations

Standard sea-level atmospheric pressure is defined as 14.6959 psi (101.325 kPa or 1 atm). However, atmospheric pressure decreases as elevation above sea level increases. For example:

• Sea Level (0 ft): P_atm ≈ 14.7 psi
• Denver, CO (5,280 ft): P_atm ≈ 12.2 psi
• High Altitude (10,000 ft): P_atm ≈ 10.1 psi

Our calculator allows entering custom local atmospheric pressure or choosing altitude presets so your PSIG to PSIA conversions remain 100% accurate anywhere on Earth.