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inHg to PSI Converter

Convert inches of mercury to PSI and back at 0.491154 psi per inHg, with kPa and millibar plus altimeter, manifold-vacuum, and full-vacuum context.

inHg to PSI Converter

Enter a non-negative pressure in inHg to convert to psi.

29.92 inHg equals

14.6953 psi

Inches of mercury

29.92 inHg

PSI

14.6953 psi

Kilopascals

101.3208 kPa

Millibar

1,013.21 mbar

Millimeters of mercury

759.97 mmHg

For context: 29.92 inHg is roughly standard sea-level pressure, 29.92 inHg (14.696 psi = 1 atm = 1013.25 mbar).

Altimeter-setting range: 28.00 to 31.00 inHg (13.75 to 15.23 psi) is the standard aviation altimeter-setting window, centered on 29.92 inHg (the International Standard Atmosphere sea-level pressure). Read this way, the value is an absolute pressure, not a vacuum.

Near full vacuum: 29 inHg or more of vacuum approaches a perfect mechanical vacuum at sea level (about 29.92 inHg below ambient). HVAC and lab pumps target this window when evacuating a system. As an absolute pressure, the same number is instead near standard sea-level barometric pressure, so confirm whether your gauge reads absolute or vacuum.

1 inHg = 0.491154 psi = 3.386389 kPa = 33.86 mbar = 25.4 mmHg. 1 psi = 2.036 inHg. Mental shortcut: roughly halve inHg to get psi, or double psi to get inHg.

Frequently Asked Questions about the inHg to PSI Converter

How do you convert inHg to psi?
Multiply inches of mercury by 0.491154 to get pounds per square inch. For example, 29.92 inHg times 0.491154 is 14.6953 psi, which is standard sea-level pressure (1 atm). To go the other way, divide psi by 0.491154 (or multiply by 2.036021) to get inHg.
Where does the 0.491154 factor come from?
The conventional inch of mercury is fixed by NIST as exactly 3386.389 pascals (a mercury column at 0 degrees Celsius under standard gravity). One psi is 6894.757293 pascals. Dividing gives 3386.389 / 6894.757293 = 0.491154 psi per inch of mercury, the factor used in aviation, barometry, and HVAC.
Is 1 inHg the same as 1 inch of vacuum?
The unit is the same, but the reference frame differs. An altimeter setting like 29.92 inHg is an absolute pressure measured from a perfect vacuum. A manifold or HVAC gauge reads inches of mercury of vacuum, meaning how far below local atmospheric pressure you are. This converter never adds or subtracts an atmosphere, so it gives the same magnitude either way. You decide whether the number is absolute or gauge.
Why is standard pressure 29.92 inHg?
The International Standard Atmosphere defines sea-level pressure as 1 atm, which equals 101325 pascals, 14.696 psi, 1013.25 millibar, and 29.92 inHg. Aviation uses 29.92 inHg (or 1013.25 hPa) as the standard altimeter setting above the transition altitude. Local barometric pressure shifts this reading up or down by roughly 1 inHg with weather and altitude changes.
What is a healthy engine manifold vacuum in inHg?
A gasoline engine at idle near sea level usually reads 15 to 22 inHg of manifold vacuum, which is 7.37 to 10.81 psi below ambient. Lower or unsteady readings can point to vacuum leaks, valve timing, or ignition issues. The reading drops at higher elevation because there is less atmospheric pressure to pull against.
How do I convert inHg to kPa or millibar?
Multiply inches of mercury by 3.386389 to get kilopascals, or by 33.86389 to get millibar (1 millibar equals 1 hectopascal). For mercury units, 1 inHg equals 25.4 mmHg because both use the same mercury density and gravity, leaving only the exact 25.4 millimeter per inch ratio. This converter shows psi, kPa, millibar, and mmHg together for any value you enter.

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