›› Convert millimeter water [4 °C] to


mm H2O
inch mercury


›› More information from the unit converter

How many mm H2O in 1 inch mercury? The answer is 345.31557667501.
We assume you are converting between millimeter water [4 °C] and .
You can view more details on each measurement unit:
mm H2O or inch mercury
The SI derived unit for pressure is the pascal.
1 pascal is equal to 0.10197162129779 mm H2O, or 0.00029529980164712 inch 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 mercury.
Type in your own numbers in the form to convert the units!


›› Quick conversion chart of mm H2O to inch mercury

1 mm H2O to inch mercury = 0.0029 inch mercury

10 mm H2O to inch mercury = 0.02896 inch mercury

50 mm H2O to inch mercury = 0.1448 inch mercury

100 mm H2O to inch mercury = 0.28959 inch mercury

200 mm H2O to inch mercury = 0.57918 inch mercury

500 mm H2O to inch mercury = 1.44795 inch mercury

1000 mm H2O to inch mercury = 2.8959 inch mercury



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›› Common pressure conversions

mm H2O to newton/square millimeter
mm H2O to foot mercury
mm H2O to hectobar
mm H2O to zeptopascal
mm H2O to kilobar
mm H2O to attopascal
mm H2O to poundal/square foot
mm H2O to millitorr
mm H2O to yoctopascal
mm H2O to gram/square centimeter


›› Definition: Inch mercury

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widely used for barometric pressure in weather reports and aviation in the United States, but is considered somewhat outdated elsewhere.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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