How to Convert PSIA to PSIG: Formula, Conversion Chart & Calculator
Learn how to convert PSIA to PSIG using the formula PSIG = PSIA - 14.7. Features calculation steps for 0, 14.7, 20, 30, 50, 100 PSIA, FAQs, and online calculator.
To convert PSIA to PSIG (Pounds per Square Inch Absolute to Pounds per Square Inch Gauge), you subtract ambient atmospheric pressure from the absolute pressure reading. Understanding how to convert PSIA to PSIG is essential when working with thermodynamic tables, HVAC evacuation gauges, or gas law calculations.
If you need quick automated conversions, our online PSIA to PSIG calculator on the homepage provides instant conversion.
1. What is PSIA and PSIG in Pressure Measurement?
- PSIA (Pounds per Square Inch Absolute): Total pressure measured relative to absolute zero pressure (a perfect vacuum).
- PSIG (Pounds per Square Inch Gauge): Pressure measured relative to ambient surrounding atmospheric air.
For a complete conceptual breakdown of zero references, read PSIG vs PSIA difference explained.
2. How to Convert PSIA to PSIG Using the Reverse Formula
To convert PSIA to PSIG, subtract atmospheric pressure ($P_{\text{atm}} = 14.7\text{ psi}$) from the absolute pressure reading:
$$\text{PSIG} = \text{PSIA} - P_{\text{atm}}$$
$$\text{PSIG} = \text{PSIA} - 14.7$$
Quick answer: How to Convert PSIA to PSIG
Answer: To convert PSIA to PSIG, subtract 14.7 from the PSIA value at sea level ($\text{PSIG} = \text{PSIA} - 14.7$). For instance, 14.7 PSIA to PSIG equals 0 PSIG, while 100 PSIA to PSIG equals 85.3 PSIG.
3. Step-by-Step Examples: How to Convert PSIA to PSIG
Here is how converting PSIA to PSIG works across key technical benchmark values:
Example 1: How to Convert 0 PSIA to PSIG (Perfect Vacuum)
$$\text{PSIG} = 0 - 14.7 = -14.7\text{ PSIG}$$
Example 2: How to Convert 1 PSIA to PSIG
$$\text{PSIG} = 1 - 14.7 = -13.7\text{ PSIG}$$
Example 3: How to Convert 10 PSIA to PSIG
$$\text{PSIG} = 10 - 14.7 = -4.7\text{ PSIG}$$
Example 4: How to Convert 14.7 PSIA to PSIG (Atmospheric Benchmark)
$$\text{PSIG} = 14.7 - 14.7 = 0\text{ PSIG}$$
Example 5: How to Convert 15 PSIA to PSIG
$$\text{PSIG} = 15 - 14.7 = 0.3\text{ PSIG}$$
Example 6: How to Convert 20 PSIA to PSIG
$$\text{PSIG} = 20 - 14.7 = 5.3\text{ PSIG}$$
Example 7: How to Convert 25 PSIA to PSIG
$$\text{PSIG} = 25 - 14.7 = 10.3\text{ PSIG}$$
Example 8: How to Convert 30 PSIA to PSIG
$$\text{PSIG} = 30 - 14.7 = 15.3\text{ PSIG}$$
Example 9: How to Convert 50 PSIA to PSIG
$$\text{PSIG} = 50 - 14.7 = 35.3\text{ PSIG}$$
Example 10: How to Convert 85 PSIA to PSIG
$$\text{PSIG} = 85 - 14.7 = 70.3\text{ PSIG}$$
Example 11: How to Convert 100 PSIA to PSIG
$$\text{PSIG} = 100 - 14.7 = 85.3\text{ PSIG}$$
4. PSIA to PSIG Conversion Lookup Chart
| Absolute Pressure (PSIA) | Formula Applied | Gauge Reading (PSIG) | Pressure Regime |
|---|---|---|---|
| 0 PSIA to PSIG | $0 - 14.7$ | -14.7 PSIG | Absolute Vacuum |
| 1 PSIA to PSIG | $1 - 14.7$ | -13.7 PSIG | Deep Vacuum Evacuation |
| 10 PSIA to PSIG | $10 - 14.7$ | -4.7 PSIG | Partial Vacuum |
| 14.7 PSIA to PSIG | $14.7 - 14.7$ | 0 PSIG | Ambient Air (Sea Level) |
| 15 PSIA to PSIG | $15 - 14.7$ | 0.3 PSIG | Near Ambient |
| 20 PSIA to PSIG | $20 - 14.7$ | 5.3 PSIG | Low Pressure Line |
| 25 PSIA to PSIG | $25 - 14.7$ | 10.3 PSIG | Low Pneumatic System |
| 30 PSIA to PSIG | $30 - 14.7$ | 15.3 PSIG | Low Pressure Tank |
| 50 PSIA to PSIG | $50 - 14.7$ | 35.3 PSIG | Automobile Tire Absolute Level |
| 85 PSIA to PSIG | $85 - 14.7$ | 70.3 PSIG | Process Piping Line |
| 100 PSIA to PSIG | $100 - 14.7$ | 85.3 PSIG | Industrial Air System |
5. Applications in Thermodynamics & Gas Laws
Thermodynamic state equations like Boyle’s Law ($P_1 V_1 = P_2 V_2$) and the Ideal Gas Law ($PV = nRT$) strictly require absolute pressure input (PSIA). Learn more in our article on gas laws and ideal gas PSIA calculations.
If you need the opposite calculation, read how to convert PSIG to PSIA or use our online PSIG to PSIA converter tool.
Related Resources
- PSIG to PSIA Tool: Homepage PSIG to PSIA Calculator – Online conversion calculator.
- PSIG to PSIA Guide: How to Convert PSIG to PSIA – Detailed formula and examples.
- Gas Laws & Thermodynamics: Gas Laws & Ideal Gas PSIA Calculations – Engineering gas laws guide.
- HVAC Systems: HVAC & Refrigeration Pressure Conversion – Refrigerant gauge conversion.
Frequently asked questions
How do you convert PSIA to PSIG?
To convert PSIA to PSIG, subtract atmospheric pressure (14.7 psi at sea level) from the absolute pressure value: PSIG = PSIA - 14.7.
What is 14.7 PSIA in PSIG?
14.7 PSIA is equal to 0 PSIG at standard sea level because 14.7 PSIA equals ambient atmospheric pressure.
What is 0 PSIA in PSIG?
0 PSIA is equal to -14.7 PSIG, representing a perfect vacuum relative to ambient atmospheric air at sea level.
How to convert 100 PSIA to PSIG?
To convert 100 PSIA to PSIG at sea level: 100 PSIA - 14.7 = 85.3 PSIG.