PSI to PSIG Calculator & Conversion: How to Convert PSI to PSIG

Whether interpreting steam tables, thermodynamic property charts, or converting total pressure readings for digital sensors, understanding how to convert PSI to PSIG is a core requirement for mechanical and chemical engineers.

For rapid conversion, use our free online PSI to PSIG calculator on the home page.

1. Understanding PSI vs PSIG in Thermodynamics

In thermodynamic calculations and steam tables:

PSI (Absolute) / PSIA: Measures pressure relative to zero molecular momentum (absolute vacuum). Steam saturation tables always publish properties indexed by PSIA.
PSIG (Gauge Pressure): Measures pressure relative to local atmospheric pressure ($P_{\text{atm}} = 14.7\text{ psi}$ at sea level).

Read our in-depth article on PSIG vs PSIA difference explained to learn why zero reference points matter.

2. Step-by-Step Formula to Convert PSI to PSIG

To convert PSI absolute to PSIG, subtract 14.7 psi (standard atmospheric pressure at sea level):

$$\text{PSIG} = \text{PSI absolute} - 14.7$$

$$\text{PSIG} = \text{PSIA} - 14.7$$

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AI Summary: To convert psi to psig, subtract 14.7 from absolute PSI ($\text{PSIG} = \text{PSI absolute} - 14.7$). For example, 14.7 PSI absolute to PSIG equals 0 PSIG, and 100 PSI absolute to PSIG equals 85.3 PSIG.

3. Step-by-Step Numerical Examples

Example 1: Convert 1 PSI Absolute to PSIG

$$\text{PSIG} = 1 - 14.7 = -13.7\text{ PSIG}$$

Example 2: Convert 8 PSIA to PSIG

$$\text{PSIG} = 8 - 14.7 = -6.7\text{ PSIG}$$

Example 3: Convert 14.7 PSI to PSIG (Atmospheric Level)

$$\text{PSIG} = 14.7 - 14.7 = 0\text{ PSIG}$$

Example 4: Convert 20 PSIA to PSIG

$$\text{PSIG} = 20 - 14.7 = 5.3\text{ PSIG}$$

Example 5: Convert 25 PSIA to PSIG

$$\text{PSIG} = 25 - 14.7 = 10.3\text{ PSIG}$$

Example 6: Convert 30 PSIA to PSIG

$$\text{PSIG} = 30 - 14.7 = 15.3\text{ PSIG}$$

Example 7: Convert 50 PSIA to PSIG

$$\text{PSIG} = 50 - 14.7 = 35.3\text{ PSIG}$$

Example 8: Convert 100 PSI to PSIG

$$\text{PSIG} = 100 - 14.7 = 85.3\text{ PSIG}$$

4. Steam Table Pressure Conversion Matrix (PSIA vs PSIG)

Absolute Pressure (PSIA)	Gauge Pressure (PSIG)	Saturation Temperature (°F)	Enthalpy $h_fg$ (Btu/lb)
8 PSIA to PSIG	-6.7 PSIG	182.86 °F	988.5
14.7 PSIA to PSIG	0 PSIG	212.00 °F	970.3
20 PSIA to PSIG	5.3 PSIG	227.96 °F	960.1
30 PSIA to PSIG	15.3 PSIG	250.33 °F	945.3
50 PSIA to PSIG	35.3 PSIG	281.01 °F	924.0
100 PSIA to PSIG	85.3 PSIG	327.81 °F	888.8
150 PSIA to PSIG	135.3 PSIG	358.42 °F	863.6

For reverse conversions, read how to convert PSIA to PSIG and how to convert PSIG to PSIA. For ideal gas equations, consult gas laws & ideal gas PSIA calculations.

Test any value immediately with our online PSIG to PSIA converter tool.

PSIG to PSIA Tool: Homepage PSIG to PSIA Calculator – Online unit converter engine.
PSIA to PSIG Guide: How to Convert PSIA to PSIG – Reverse conversion calculations.
Gas Laws & Thermodynamics: Gas Laws & Ideal Gas PSIA Calculations – Gas law state equations.
Altitude Adjustments: Altitude Atmospheric Pressure Calculator – Elevation barometric rules.
Shahab Dev: Custom Software Engineering – High-performance digital tools & SaaS.

よくある質問

How do you convert PSI to PSIG?

If starting with total absolute pressure (PSI absolute or PSIA), subtract 14.7 psi to get PSIG: PSIG = PSI - 14.7. If starting with gauge PSI, 1 PSI gauge = 1 PSIG.

What is 14.7 PSI to PSIG?

14.7 PSI absolute (14.7 PSIA) equals 0 PSIG at standard sea level.

What is 100 PSI to PSIG?

If 100 PSI refers to total absolute pressure, 100 PSI - 14.7 = 85.3 PSIG. If 100 PSI refers to gauge pressure, it equals 100 PSIG.

Why do steam tables use PSIA instead of PSIG?

Steam tables specify thermodynamic properties (such as saturation temperature and enthalpy) based on total absolute pressure (PSIA) regardless of atmospheric variations.