›› Convert millimeter water [4 °C] to inch of mercury [0 °C]

mm H2O
inch of mercury

›› More information from the unit converter

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!

›› Quick conversion chart of mm H2O to inch of mercury

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

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

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›› Common pressure conversions

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

›› Definition: Inch of 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widely used for barometric pressure in weather reports and aviation in the United States, but is considered somewhat outdated elsewhere.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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ConvertUnits.com provides an online conversion calculator for all types of measurement units. You can find metric conversion tables for SI units, as well as English units, currency, and other data. Type in unit symbols, abbreviations, or full names for units of length, area, mass, pressure, and other types. Examples include mm, inch, 100 kg, US fluid ounce, 6'3", 10 stone 4, cubic cm, metres squared, grams, moles, feet per second, and many more!