Inch of mercury
Inches of mercury, inHg or "Hg 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widely used for barometric pressure in weather reports and aviation in the United States, but is considered somewhat outdated elsewhere.
- 1 inHg = 3,386.389 pascals at 0 °C.
Aircraft operating at higher altitudes (at or above what is called the Transition Altitude, which varies by country) 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.
In older literature, an inch of mercury based on the height of a column at 60 °F (15.6 °C) was common.
- 1 inHg60 °F = 3,376.85 Pa