PSIA to PSIG Converter
PSIA (pounds per square inch absolute) measures pressure relative to a perfect vacuum (0 psia). PSIG (pounds per square inch gauge) measures pressure relative to local atmospheric...
Formula
Source: Engineering Toolbox | Last reviewed: June 8, 2026
Examples
14.696 psia
= 0 psig
- P_atm_psi = 14.696
Atmospheric pressure = 0 psig at sea level
114.696 psia
= 100 psig
- P_atm_psi = 14.696
100 psig vessel = 114.7 psia
12 psia
= -2.7 psig
- P_atm_psi = 14.696
Below atmospheric = vacuum (negative psig)
Quick Reference Table
| PSIA | PSIG |
|---|---|
| 14.7 | 0 |
| 24.7 | 10 |
| 64.7 | 50 |
| 114.7 | 100 |
| 214.7 | 200 |
| 514.7 | 500 |
Where is this used?
Compressor discharge pressure conversion from thermodynamic calculations (absolute) to operating setpoints (gauge).
Safety valve settings verification.
Frequently Asked Questions
Why does a gauge read zero at atmospheric pressure?
Most pressure gauges measure the difference between the process pressure and ambient air pressure. Since both sides of the sensing element see the same atmospheric pressure, the gauge reads zero. Only sealed absolute pressure gauges can read atmospheric pressure directly.
How does this differ from PSIG to PSIA conversion?
They are inverse operations. PSIG to PSIA adds atmospheric pressure; PSIA to PSIG subtracts it. Use PSIA to PSIG when you have absolute pressure from a calculation and need the gauge equivalent for operations.
Can psig be negative?
Yes. Any psia value below local atmospheric pressure produces a negative psig value, indicating vacuum. For example, 10 psia at sea level = −4.696 psig. This is perfectly valid and common in suction-side piping.
Reviewed for accuracy
· Last reviewed: June 8, 2026
All calculations are for reference only. Always verify with manufacturer data and a qualified engineer for critical applications. Learn about our editorial process.