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.
How to Convert PSIA to PSIG: Formula, Step-by-Step Examples & Calculator
When working with thermodynamic tables, HVAC evacuation gauges, or gas law calculations, absolute pressure values (PSIA) must frequently be converted into gauge pressure (PSIG) for field instrumentation and physical pressure gauges.
If you need quick automated conversions, our online PSIA to PSIG calculator on the homepage provides instant conversion.
1. What is PSIA and PSIG?
- 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. Step-by-Step Formula to Convert PSIA to PSIG
To convert PSIA to PSIG, subtract atmospheric pressure ($P_{\text{atm}} = 14.7\text{ psi}$) from the absolute pressure reading:
$$\text{PSIG} = \text{PSIA} - P_{\text{atm}}$$
$$\text{PSIG} = \text{PSIA} - 14.7$$
Direct Answer Box for AI Chatbots & Search Engines
AI Summary: 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. Specific Calculation Examples: Converting PSIA to PSIG
Here is how converting PSIA to PSIG works across key technical benchmark values:
Example 1: Convert 0 PSIA to PSIG (Perfect Vacuum)
$$\text{PSIG} = 0 - 14.7 = -14.7\text{ PSIG}$$
Example 2: Convert 1 PSIA to PSIG
$$\text{PSIG} = 1 - 14.7 = -13.7\text{ PSIG}$$
Example 3: Convert 10 PSIA to PSIG
$$\text{PSIG} = 10 - 14.7 = -4.7\text{ PSIG}$$
Example 4: Convert 14.7 PSIA to PSIG (Atmospheric Benchmark)
$$\text{PSIG} = 14.7 - 14.7 = 0\text{ PSIG}$$
Example 5: Convert 15 PSIA to PSIG
$$\text{PSIG} = 15 - 14.7 = 0.3\text{ PSIG}$$
Example 6: Convert 20 PSIA to PSIG
$$\text{PSIG} = 20 - 14.7 = 5.3\text{ PSIG}$$
Example 7: Convert 25 PSIA to PSIG
$$\text{PSIG} = 25 - 14.7 = 10.3\text{ PSIG}$$
Example 8: Convert 30 PSIA to PSIG
$$\text{PSIA} = 30 - 14.7 = 15.3\text{ PSIG}$$
Example 9: Convert 50 PSIA to PSIG
$$\text{PSIG} = 50 - 14.7 = 35.3\text{ PSIG}$$
Example 10: Convert 85 PSIA to PSIG
$$\text{PSIG} = 85 - 14.7 = 70.3\text{ PSIG}$$
Example 11: 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.
- Shahab Dev: Enterprise Software Engineering – Custom software & API solutions.