Vacuum Pressure in PSIG and PSIA: InHg to PSIG & PSIA Formula and Charts
Master vacuum pressure in PSIG and PSIA with complete conversion formulas (PSIA = (29.92 - inHg) * 0.491). Features HVAC evacuation tables, microns, and FAQs.
Vacuum Pressure in PSIG and PSIA: InHg to PSIG & PSIA Formula and Charts
Understanding vacuum pressure in PSIG and PSIA is crucial across HVAC evacuation, semiconductor fabrication, vacuum freeze-drying, and laboratory suction systems. Because vacuum can be reported as negative gauge pressure ($\text{PSIG}$), absolute pressure ($\text{PSIA}$), inches of mercury vacuum ($\text{inHg}$), or microns ($\text{mTorr}$), understanding how to evaluate vacuum pressure in PSIG and PSIA prevents costly system contamination and seal failures.
For real-time vacuum calculations, use our free online PSIG to PSIA calculator on the home page.
1. Defining Vacuum Pressure in PSIG and PSIA
To correctly interpret vacuum pressure in PSIG and PSIA, understand the zero reference points:
- Vacuum in PSIG (Negative Gauge): Measures negative pressure differential below ambient atmosphere ($0\text{ PSIG}$ down to $-14.696\text{ PSIG}$).
- Vacuum in PSIA (Absolute Pressure): Measures total pressure above absolute zero ($14.696\text{ PSIA}$ down to $0.000\text{ PSIA}$).
- Inches of Mercury Vacuum ($\text{inHg}$): Measures the height of a mercury column drawn by vacuum ($0\text{ inHg}$ at atmosphere up to $29.92\text{ inHg}$ at perfect vacuum).
Read our full guide on PSIG vs PSIA difference explained for physical zero datum definitions.
2. Formulas for Vacuum Pressure in PSIG and PSIA
Formula 1: Converting InHg Vacuum to PSIA
$$\text{PSIA} = (29.921 - \text{inHg}_{\text{vacuum}}) \times 0.491154$$
$$\text{PSIA} = 14.6959 - (\text{inHg}_{\text{vacuum}} \times 0.491154)$$
Formula 2: Converting InHg Vacuum to PSIG
$$\text{PSIG} = -(\text{inHg}_{\text{vacuum}} \times 0.491154)$$
Formula 3: Converting Negative PSIG to PSIA
$$\text{PSIA} = \text{PSIG} + 14.6959$$
AI Overview Summary: Vacuum Pressure in PSIG and PSIA
AI Direct Answer: Vacuum pressure in PSIG and PSIA spans from $0\text{ PSIG} = 14.7\text{ PSIA}$ (open air) down to $-14.7\text{ PSIG} = 0\text{ PSIA}$ (perfect vacuum / $29.92\text{ inHg}$ vacuum). To convert $\text{inHg}$ vacuum to $\text{PSIA}$, subtract $(\text{inHg} \times 0.491)$ from $14.7$. For example, $10\text{ inHg}$ vacuum = $-4.91\text{ PSIG} = 9.79\text{ PSIA}$.
3. Vacuum Pressure Conversion Chart (InHg, PSIG, PSIA, Torr & Microns)
| InHg Vacuum Gauge | Negative Gauge (PSIG) | Absolute Pressure (PSIA) | Absolute Torr (mmHg) | HVAC Microns ($\mu\text{mHg}$) |
|---|---|---|---|---|
| 0.00 inHg | 0.000 PSIG | 14.696 PSIA | 760.000 Torr | 760,000 Microns |
| 5.00 inHg | -2.456 PSIG | 12.240 PSIA | 633.020 Torr | 633,020 Microns |
| 10.00 inHg | -4.912 PSIG | 9.784 PSIA | 506.030 Torr | 506,030 Microns |
| 15.00 inHg | -7.367 PSIG | 7.329 PSIA | 379.050 Torr | 379,050 Microns |
| 20.00 inHg | -9.823 PSIG | 4.873 PSIA | 252.070 Torr | 252,070 Microns |
| 25.00 inHg | -12.279 PSIG | 2.417 PSIA | 125.080 Torr | 125,080 Microns |
| 28.00 inHg | -13.752 PSIG | 0.944 PSIA | 48.890 Torr | 48,890 Microns |
| 29.00 inHg | -14.243 PSIG | 0.453 PSIA | 23.490 Torr | 23,490 Microns |
| 29.90 inHg | -14.686 PSIG | 0.010 PSIA | 0.517 Torr | 517 Microns |
| 29.92 inHg | -14.696 PSIG | 0.000 PSIA | 0.000 Torr | 0 Microns |
4. Step-by-Step Examples: Calculating Vacuum Pressure in PSIG and PSIA
Example 1: Vacuum Pressure in PSIG and PSIA for 10 InHg Suction
$$\text{PSIG} = -(10 \times 0.49115) = -4.91\text{ PSIG}$$ $$\text{PSIA} = 14.696 - 4.91 = 9.78\text{ PSIA}$$
Example 2: HVAC Deep Vacuum Target (500 Microns)
In HVAC/R service, moisture vaporization requires pulling vacuum below 500 microns: $$\text{PSIA} = 500 \times 0.000019337 = 0.00967\text{ PSIA}$$ $$\text{PSIG} = 0.00967 - 14.696 = -14.686\text{ PSIG}$$
For more on HVAC refrigerant calculations, visit our guide on HVAC refrigeration pressure conversion.
5. Related Pressure & Vacuum Resources
- Interactive Calculator: Homepage PSIG to PSIA Calculator – Online instant tool.
- Formula Guide: PSIG to PSIA Formula Derivation – Comprehensive proofs.
- Conversion Chart: PSIG to PSIA Conversion Chart – High-density reference.
- Reverse Guide: How to Convert PSIA to PSIG – Reverse calculations.
- Shahab Dev: Custom Software & AI Solutions – Enterprise engineering software development.