Inch mercury to Psi Converter
Enter the value that you want to convert inch mercury (inHg) to psi or psi to inch mercury.
1 inch mercury = 0.4911529 psi
Formula: psi = inch mercury value × 0.4911529
inch mercury to psi
10 inch mercury = 4.91153 psi
Popular Pressure Converters:
Inch mercury vs Psi
What is Inch mercury?
Inch mercury (inHg) is a unit of pressure measurement. 1 inch mercury is equal to 0.4911529 psi.
What is Psi?
Psi (psi) is a unit of pressure measurement. 1 psi is equal to 2.0360259 inch mercury.
Pressure Units Across Industries
Pressure measurements vary dramatically by industry. Meteorologists report in millibars or hectopascals, tire shops use PSI, scuba divers think in atmospheres or bar, vacuum engineers work in torr, and hydraulic systems specify in megapascals. A single industrial plant might encounter all these units across different equipment manuals, safety datasheets, and regulatory standards from different countries.
inch mercury to psi metric conversion table
| 0.01 inHg | = | 0.00491 psi |
| 0.1 inHg | = | 0.04912 psi |
| 1 inHg | = | 0.49115 psi |
| 2 inHg | = | 0.98231 psi |
| 3 inHg | = | 1.47346 psi |
| 4 inHg | = | 1.96461 psi |
| 5 inHg | = | 2.45576 psi |
| 6 inHg | = | 2.94692 psi |
| 7 inHg | = | 3.43807 psi |
| 8 inHg | = | 3.92922 psi |
| 9 inHg | = | 4.42038 psi |
| 10 inHg | = | 4.91153 psi |
| 11 inHg | = | 5.40268 psi |
| 12 inHg | = | 5.89383 psi |
| 13 inHg | = | 6.38499 psi |
| 14 inHg | = | 6.87614 psi |
| 15 inHg | = | 7.36729 psi |
| 16 inHg | = | 7.85845 psi |
| 17 inHg | = | 8.34960 psi |
| 18 inHg | = | 8.84075 psi |
| 19 inHg | = | 9.33190 psi |
| 20 inHg | = | 9.82306 psi |
| 30 inHg | = | 14.73459 psi |
| 40 inHg | = | 19.64612 psi |
| 50 inHg | = | 24.55764 psi |
| 60 inHg | = | 29.46917 psi |
| 70 inHg | = | 34.38070 psi |
| 80 inHg | = | 39.29223 psi |
| 90 inHg | = | 44.20376 psi |
| 100 inHg | = | 49.11529 psi |
| 200 inHg | = | 98.23058 psi |
| 300 inHg | = | 147.34587 psi |
| 400 inHg | = | 196.46116 psi |
| 500 inHg | = | 245.57645 psi |
| 600 inHg | = | 294.69174 psi |
| 700 inHg | = | 343.80703 psi |
| 800 inHg | = | 392.92232 psi |
| 900 inHg | = | 442.03760 psi |
| 1000 inHg | = | 491.15289 psi |
How to Convert Inch mercury to Psi?
We can convert inch mercury to psi by using an example.
Example:
Convert 20 Inch mercury to Psi?
We know 1 Inch mercury = 0.4911529 psi; 1 Psi = 2.0360259 inch mercury.
20 inch mercury = ___psi
20 × 0.4911529 = 9.82306 psi (we know 1 inch mercury = 0.4911529 psi)
Answer:
20 inch mercury = 9.82306 psi
How to Convert Inches of Mercury to PSI (Step-by-Step)
Converting inches of mercury (inHg) to PSI keeps both values in US customary units — useful for HVAC, automotive, and industrial vacuum work where technicians use PSI gauges. The conversion factor is 1 inHg = 0.491154 PSI.
- Write down the pressure value in inches of mercury (inHg).
- Multiply the inHg value by 0.491154.
- The result is the equivalent pressure in PSI.
- For quick estimation, multiply by 0.49 or approximately 0.5 (overshoots by ~1.8%).
Common Inches of Mercury to PSI Conversions
Vacuum and barometric readings in inHg translated to the PSI scale.
| Inch mercury | Psi |
|---|---|
| 1 inHg | 0.491 PSI |
| 5 inHg | 2.456 PSI |
| 10 inHg | 4.912 PSI |
| 15 inHg | 7.367 PSI |
| 20 inHg | 9.823 PSI |
| 25 inHg | 12.279 PSI |
| 29.92 inHg | 14.696 PSI |
Solved Examples: inHg to PSI
Question 1: An HVAC gauge shows 28 inHg vacuum during system evacuation. What is the absolute pressure in PSI?
Solution:
Absolute pressure = 29.92 - 28 = 1.92 inHg
Pressure in PSI = 1.92 × 0.491154
= 0.943 PSI absolute
Answer: 28 inHg vacuum = 0.943 PSIA — a deep vacuum suitable for initial evacuation.
Question 2: A brake booster requires at least 18 inHg vacuum to operate. What gauge pressure difference in PSI does this represent?
Solution:
Pressure difference = 18 inHg × 0.491154
= 8.84 PSI
Answer: 18 inHg = 8.84 PSI of vacuum assist — the force multiplier for brake pedal effort.
Question 3: Convert barometric pressure of 30.15 inHg to PSI.
Solution:
Pressure in PSI = 30.15 × 0.491154
= 14.808 PSI
Answer: 30.15 inHg = 14.81 PSI — slightly above standard atmospheric pressure.
Question 4: A vacuum packaging machine operates at 26 inHg. What is this as gauge PSI below atmospheric?
Solution:
Vacuum in PSI = 26 × 0.491154
= 12.77 PSI below atmospheric
Answer: 26 inHg vacuum = 12.77 PSI vacuum (or 14.70 - 12.77 = 1.93 PSIA).
Practice Questions: inHg to PSI
Try solving these on your own to test your understanding:
- Convert 29.92 inHg to PSI. (Answer: 14.696 PSI)
- A vacuum gauge reads 22 inHg. Express as PSI vacuum. (Answer: 10.81 PSI)
- Convert 15 inHg to PSI. (Answer: 7.37 PSI)
- A compressor inlet vacuum is 3 inHg. What is this in PSI? (Answer: 1.47 PSI)
- Convert 30.50 inHg to PSI. (Answer: 14.98 PSI)
Brake Booster and Engine Vacuum in PSI
Automotive technicians measure engine vacuum in inHg but sometimes need PSI equivalents for calculations. A healthy engine at idle produces 17-22 inHg vacuum (8.3-10.8 PSI). The brake booster needs at least 15-18 inHg (7.4-8.8 PSI) to provide adequate power assist. At wide-open throttle, vacuum drops to near zero. Turbocharged engines in boost produce positive pressure, often measured in PSI directly (10-25 PSI boost = 20.4-50.9 inHg above atmospheric).
HVAC Evacuation: Reading Vacuum in inHg and PSI
When evacuating refrigeration systems, technicians use compound gauges reading from 30 inHg vacuum through 0 to positive PSI. The blue (low-side) gauge typically shows both scales. Good practice requires pulling below 500 microns (verified by a digital micron gauge), but the analog compound gauge gets the system from atmospheric to deep vacuum. At 29 inHg vacuum, the system is at 14.7 - 14.25 = 0.45 PSIA — already very close to a complete vacuum by industrial standards.
Key Takeaways
- Multiply inHg by 0.491154 to get PSI.
- Quick shortcut: 2 inHg ≈ 1 PSI (1.8% error).
- Standard atmosphere: 29.92 inHg = 14.696 PSI.
- Engine idle vacuum: 18-22 inHg = 8.8-10.8 PSI.
- For vacuum readings: absolute PSI = atmospheric PSI minus vacuum PSI.
- Compound gauges show both inHg vacuum and positive PSI on the same dial.
Inch mercury to Psi Conversion Formula
psi = inch mercury × 0.4911529
1 inch mercury = 0.4911529 psi
1 psi = 2.0360259 inch mercury
Reverse: inch mercury = psi × 2.0360259
Frequently Asked Questions
How many psi are in 1 inch mercury?
There are 0.4911529 psi in 1 inch mercury. To convert inch mercury to psi, multiply the value by 0.4911529.
How do I convert inch mercury to psi?
Multiply your inch mercury value by 0.4911529 to get the equivalent in psi. For example, 5 inch mercury = 5 × 0.4911529 = 2.45576 psi.
How do I convert psi to inch mercury?
Multiply your psi value by 2.0360259 to get the equivalent in inch mercury. Alternatively, divide by 0.4911529.
What is 10 inch mercury in psi?
10 inch mercury is equal to 4.91153 psi.
What is 100 inch mercury in psi?
100 inch mercury is equal to 49.11529 psi.