How many mm H2O in 1 inch of mercury?
The answer is 345.31554268447.

We assume you are converting between **millimeter water [4 °C]** and **inch of mercury [0 °C]**.

You can view more details on each measurement unit:

mm H2O or
inch of mercury

The SI derived unit for **pressure** is the pascal.

1 pascal is equal to 0.10197162129779 mm H2O, or 0.00029529983071445 inch of mercury.

Note that rounding errors may occur, so always check the results.

Use this page to learn how to convert between millimeters water and inches of mercury.

Type in your own numbers in the form to convert the units!

1 mm H2O to inch of mercury = 0.0029 inch of mercury

10 mm H2O to inch of mercury = 0.02896 inch of mercury

50 mm H2O to inch of mercury = 0.1448 inch of mercury

100 mm H2O to inch of mercury = 0.28959 inch of mercury

200 mm H2O to inch of mercury = 0.57918 inch of mercury

500 mm H2O to inch of mercury = 1.44795 inch of mercury

1000 mm H2O to inch of mercury = 2.8959 inch of mercury

You can do the reverse unit conversion from inch of mercury to mm H2O, or enter any two units below:

mm H2O to femtobar

mm H2O to foot mercury

mm H2O to exabar

mm H2O to kilobar

mm H2O to barad

mm H2O to foot of air

mm H2O to millibar

mm H2O to meganewton/square meter

mm H2O to picobar

mm H2O to sthene/square meter

Inches of mercury or inHg is a non-SI unit for pressure. It is still widely used for barometric pressure in weather reports and aviation in the United States, but is considered somewhat outdated elsewhere.

It is defined as the pressure exerted by a column of mercury of 1 inch in height at 32 °F (0 °C) at the standard acceleration of gravity.

1 inHg = 3,386.389 pascals at 0 °C.

Aircraft operating at higher altitudes (above 18,000 feet) set their barometric altimeters to a standard pressure of 29.92 inHg or 1,013.2 hPa (1 hPa = 1 mbar) regardless of the actual sea level pressure, with inches of mercury used in the U.S. and Canada. The resulting altimeter readings are known as flight levels.

Piston engine aircraft with constant-speed propellers also use inHg to measure manifold pressure, which is indicative of engine power produced.

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