inHg to PSI Converter

To convert inches of mercury to psi, multiply by 0.491154, or divide by 2.03602. 30 inHg is 14.7346 psi. inHg is the unit of US barometric pressure, altimeter settings and vacuum gauges.

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How It Works

An inch of mercury is the pressure at the bottom of a column of mercury one inch high. The conventional unit fixes the mercury at 13,595.1 kg/m³ (its density at 0 °C) under standard gravity, which makes 1 inHg = 3,386.39 Pa.

On a vacuum gauge, the reading is the drop below the surrounding atmosphere, so it converts to psi of vacuum with the same factor. For absolute pressure, take it away from atmospheric pressure: at sea level that is 14.6959 psi, or 29.9213 inHg.

Formula

psi = inHg × 0.491154

The factor is the conventional inch of mercury (3,386.39 Pa) divided by the pound-force per square inch (6,894.76 Pa), the values in NIST SP 811. Tables for inHg at 60 °F, used in some US gas measurement, give a slightly smaller factor.

Worked Example

A barometer reads 29.53 inHg:

29.53 × 0.491154 = 14.5038 psi

inHg to PSI Table

inHg psi kPa mbar
1 inHg 0.491154 psi 3.38639 kPa 33.8639 mbar
2 inHg 0.982308 psi 6.77278 kPa 67.7278 mbar
5 inHg 2.45577 psi 16.9319 kPa 169.319 mbar
10 inHg 4.91154 psi 33.8639 kPa 338.639 mbar
15 inHg 7.36731 psi 50.7958 kPa 507.958 mbar
20 inHg 9.82308 psi 67.7278 kPa 677.278 mbar
25 inHg 12.2789 psi 84.6597 kPa 846.597 mbar
28 inHg 13.7523 psi 94.8189 kPa 948.189 mbar
29 inHg 14.2435 psi 98.2053 kPa 982.053 mbar
29.92 inHg 14.6953 psi 101.321 kPa 1,013.21 mbar
30 inHg 14.7346 psi 101.592 kPa 1,015.92 mbar

Going the other way? Use the psi to inHg converter. For draught, duct and gas pressures read in inches of water, use the inches of water to psi converter.

FAQ

Common questions about converting inches of mercury to psi.

Frequently Asked Questions

How do I convert inHg to psi?

Multiply inHg by 0.491154. For example, 29.92 inHg × 0.491154 = 14.6953 psi.

How many psi is 1 inHg?

1 inHg is 0.491154 psi, or 3.38639 kPa. Two inches of mercury come to just under 1 psi.

What is 30 inHg in psi?

30 inHg is 14.7346 psi, a little above standard atmospheric pressure, which is 29.9213 inHg or 14.6959 psi.

How do I convert inHg vacuum to psi?

A vacuum gauge reads how far below atmospheric pressure the system is, so each inHg of vacuum is 0.491154 psi of vacuum. For absolute pressure, take the vacuum away from atmospheric: at sea level, 20 inHg of vacuum leaves 4.8729 psia (14.696 psi less 9.8231 psi).

Is inHg the same as inches of water?

No. Mercury is 13.6 times as dense as water, so 1 inHg equals 13.5951 inches of water (in H2O). In the US, HVAC static pressures and gas supply pressures are usually given in inches of water.

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