PSI to inHg Converter
To convert psi to inches of mercury, multiply by 2.03602, or divide by 0.491154. 10 psi is 20.3602 inHg. Use it to read a pressure in psi on a barometer, altimeter setting or vacuum gauge scaled in inHg.
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How It Works
One psi holds up a column of conventional mercury 2.03602 inches high: mercury at 13,595.1 kg/m³ under standard gravity. Because mercury is so dense, inHg suits pressures near and below atmospheric, which is why vacuum pumps, refrigeration gauges and US weather reports use it.
Formula
inHg = psi × 2.03602
The factor is the pound-force per square inch (6,894.76 Pa) divided by the conventional inch of mercury (3,386.39 Pa), the values in NIST SP 811. Tables based on inHg at 60 °F, used in some US gas measurement, give a slightly larger factor.
Worked Example
A vacuum system is held 12 psi below atmospheric pressure:
12 × 2.03602 = 24.4322 inHg of vacuum
PSI to inHg Table
| psi | inHg | mmHg |
|---|---|---|
| 0.1 psi | 0.203602 inHg | 5.17149 mmHg |
| 0.5 psi | 1.01801 inHg | 25.8575 mmHg |
| 1 psi | 2.03602 inHg | 51.7149 mmHg |
| 2 psi | 4.07204 inHg | 103.43 mmHg |
| 3 psi | 6.10806 inHg | 155.145 mmHg |
| 5 psi | 10.1801 inHg | 258.575 mmHg |
| 7.5 psi | 15.2702 inHg | 387.862 mmHg |
| 10 psi | 20.3602 inHg | 517.149 mmHg |
| 12 psi | 24.4322 inHg | 620.579 mmHg |
| 14.7 psi | 29.9295 inHg | 760.209 mmHg |
| 15 psi | 30.5403 inHg | 775.724 mmHg |
Going the other way? Use the inHg to psi converter. For lower pressures in inches of water, use the psi to inches of water converter.
FAQ
Common questions about converting psi to inches of mercury.
Frequently Asked Questions
How do I convert psi to inHg?
Multiply psi by 2.03602. For example, 14.7 psi × 2.03602 = 29.9295 inHg.
How many inHg is 1 psi?
1 psi is 2.03602 inHg, or 51.7149 mmHg. A rough rule is 2 inHg per psi.
What is atmospheric pressure in inHg?
Standard atmospheric pressure is 14.6959 psi, which is 29.9213 inHg, usually rounded to 29.92 inHg on barometers and altimeter settings.
How do I convert psi of vacuum to inHg?
Multiply the vacuum in psi by 2.03602. A suction 5 psi below atmospheric reads 10.1801 inHg on a vacuum gauge. Full vacuum at sea level is about 29.92 inHg.
Should I use psia or psig when converting to inHg?
Use whichever the inHg figure stands for. A barometer reads absolute pressure, so convert psia. A vacuum gauge reads the drop below atmospheric, so convert the psi of vacuum, which is atmospheric pressure minus the absolute pressure.
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