Inches of mercury, inHg, or ″Hg is a unit of measurement for pressure. It is still widely used for barometric pressure in weather reports and aviation in the United States, but is seldom used 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.
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.
Piston engine aircraft with constant-speed propellers also use inches of mercury to measure manifold pressure, which is indicative of engine power produced.
In older literature, an inch of mercury based on the height of a column at 60 °F (15.6 °C) was common.[1]
In English units: 1 inHg = 0.491098 psi, or 2.036254 inHg = 1 psi.
Inches of mercury, inHg or Hg is a non-SI unit for pressure, or a way to measure how hard something is pushing on something else. It is a unit that is still used a lot for counting barometric pressure, or how thick the air is in one place, in weather forecasts and aviation, or anything that has to do with flying in the United States, but is considered a bit old in other countries.
It is the amount of pressure that a column of mercury that is one inch tall has at 32 °F (0 °C) at the standard acceleration of gravity, or how fast things speed up as they are falling because of gravity.
Airplanes that are flying at high altitudes, or that are flying higher than what is called the Transition Altitude, which varies by country set their barometric altimeters, which control the air pressure in their plane, to a standard pressure of 29.92 inHg or 1,013.2 hPa (1 hPa = 1 mbar) no matter what the actual sea level pressure is, in inches of mercury used in the U.S. and Canada, and in other units in other countries. The resulting altimeter readings, or the things that show up on the plane's altimeter are known as flight levels.
   | Conversion of inHg in other units - unit-converter.org - Converter for units of measurement |
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