If you’ve ever looked at an air compressor gauge or a spec sheet, you’ve probably seen terms like PSI, PSIA, and PSIG. At first glance they look almost identical, but the differences matter—especially in engineering, HVAC, and compressed air applications. Choosing the wrong scale can lead to misreadings, underpowered systems, or even safety risks.
In this guide, we’ll break down exactly what each unit means, when to use it, and recommend the best gauges and meters that measure pressure accurately.
Quick Picks: Best Pressure Measurement Tools
- Best Overall: Ashcroft Digital Pressure Gauge (0–300 PSI, PSIA & PSIG) – Professional-grade accuracy with switchable units.
- Best Budget: WIKA 232.50 Industrial Pressure Gauge – Rugged analog gauge, available in PSIG scales, widely used in industry.
- Best Premium: Fluke 700G Digital Pressure Gauge – Lab-grade accuracy for calibration and engineering use.
Buyer’s Guide: Understanding PSI, PSIA, and PSIG
Here’s what each unit means and when to use it:
- PSI (Pounds per Square Inch): A general term for pressure measurement. By itself, PSI is not specific—it can refer to absolute or gauge pressure depending on context.
- PSIA (Pounds per Square Inch Absolute): Measures pressure relative to a perfect vacuum (zero reference point). Always includes atmospheric pressure (~14.7 PSI at sea level). Used in scientific and engineering applications.
- PSIG (Pounds per Square Inch Gauge): Measures pressure relative to atmospheric pressure. A gauge showing 0 PSIG is actually at 14.7 PSIA at sea level. This is the standard for air compressor gauges, car tires, and most everyday applications.
Example: If your compressor gauge reads 100 PSIG, the absolute pressure inside the tank is 100 + 14.7 = 114.7 PSIA.
Detailed Product Reviews
1. Ashcroft Digital Pressure Gauge (0–300 PSI)
Who it’s for: Professionals needing both PSIA and PSIG readings in one tool.
- Key Benefits: Switchable units, backlit digital display, NIST-traceable accuracy.
- Pros: Reliable, precise, easy to read in any environment.
- Cons: Higher cost than basic analog gauges.
Final Verdict: Best all-around digital gauge for serious users. Check Price
2. WIKA 232.50 Industrial Pressure Gauge
Who it’s for: Shops and facilities needing a rugged, long-lasting PSIG gauge.
- Key Benefits: Stainless steel case, filled for vibration resistance, up to 300 PSI scale.
- Pros: Durable, widely available, affordable for its quality.
- Cons: Limited to gauge pressure (PSIG only).
Final Verdict: The go-to analog gauge for industrial use. See Price
3. Fluke 700G Digital Pressure Gauge
Who it’s for: Engineers and labs requiring extremely accurate readings.
- Key Benefits: Accuracy up to 0.05% of full scale, multiple pressure unit options.
- Pros: Exceptional accuracy, trusted brand, calibration-ready.
- Cons: Expensive, overkill for casual users.
Final Verdict: Best premium option for calibration and testing. Check Price
4. Crystal Engineering XP2i Digital Test Gauge
Who it’s for: Calibration professionals and field engineers.
- Key Benefits: Ultra-accurate, rugged build, multiple units of measure.
- Pros: Military-grade durability, data logging capability.
- Cons: Very expensive.
Final Verdict: The gold standard for field calibration. View Price
5. Omega Engineering Digital Pressure Gauge
Who it’s for: Facilities needing reliable PSIG monitoring in process systems.
- Key Benefits: Digital accuracy, multiple ranges, compact design.
- Pros: Reliable, affordable digital option, easy to integrate.
- Cons: Not as accurate as Fluke or Crystal models.
Final Verdict: Great mid-range digital choice for industrial setups. See Price
6. Winters PEM Series Pressure Gauge
Who it’s for: Budget-conscious buyers needing a durable PSIG gauge.
- Key Benefits: Dual scale (PSI/bar), brass internals, reliable performance.
- Pros: Affordable, rugged, widely used in HVAC and shop compressors.
- Cons: Analog-only, no PSIA scale.
Final Verdict: A practical choice for everyday compressor use. Check Price
Comparison Table
| Product | Type | Range | Measures | Price |
|---|---|---|---|---|
| Ashcroft Digital Gauge | Digital | 0–300 PSI | PSIA & PSIG | Check Price |
| WIKA 232.50 | Analog | 0–300 PSI | PSIG | See Price |
| Fluke 700G | Digital | Varies | Multiple units | Check Price |
| Crystal XP2i | Digital | Up to 10,000 PSI | Multiple units | View Price |
| Omega Digital | Digital | 0–300 PSI | PSIG | See Price |
| Winters PEM | Analog | 0–300 PSI | PSIG | Check Price |
Frequently Asked Questions
What’s the difference between PSI, PSIA, and PSIG?
PSI is a general term. PSIA measures against a perfect vacuum (absolute), while PSIG measures against atmospheric pressure (gauge).
Why does my compressor use PSIG?
Because most tools and compressors operate relative to the atmosphere. A tire at 32 PSIG is actually 46.7 PSIA, but we only care about the gauge pressure.
When should I use PSIA instead of PSIG?
Use PSIA for scientific, vacuum, and engineering calculations where absolute accuracy matters. Use PSIG for everyday applications like tires, compressors, and shop tools.
Does altitude affect pressure readings?
Yes. At higher altitudes, atmospheric pressure drops, so PSIA changes, but PSIG remains the same because it’s relative to local atmosphere.
Conclusion
Understanding PSIA vs PSIG vs PSI is key to reading gauges correctly and choosing the right tools for your setup. For most shop and automotive uses, PSIG is the standard. For engineering, calibration, and lab work, PSIA matters.
The Ashcroft Digital Gauge is the best all-around choice, the WIKA 232.50 is a rugged budget analog gauge, and the Fluke 700G is the premium pick for precision applications.
Check today’s best gauges for PSIA, PSIG, and PSI here