How many in Hg in 1 mm Hg?
The answer is 0.0393700791974.

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

You can view more details on each measurement unit:

in Hg or
mm Hg

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

1 pascal is equal to 0.000295299830714 in Hg, or 0.00750061561303 mm Hg.

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

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

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

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widely used for barometric pressure in weather reports and aviation in the United States, but is considered somewhat outdated elsewhere.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

The torr (symbol: Torr) or millimetre of mercury (mmHg) is a non-SI unit of pressure. It is the atmospheric pressure that supports a column of mercury 1 millimetre high. The unit is named after Evangelista Torricelli, Italian physicist and mathematician, for his discovery of the principle of the barometer in 1643.

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