**Full name:** inch of mercury [0 °C]

**Plural form:** inches of mercury

**Symbol:** inHg

**Alternate spelling:** inch Hg

**Category type:** pressure

**Scale factor:** 3386.38866667

The SI derived unit for pressure is the pascal.

1 pascal is equal to 0.000295299830714 inches of mercury.

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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widely used for barometric pressure in weather reports and aviation in the United States, but is considered somewhat outdated elsewhere.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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inches of mercury to foot of air [0 °C]