Inch of mercury

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 (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 (1 atm = 29.92 inHg) or 1,013.25 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 automobile racing, particularly USAC and CART Indy car racing, inches of mercury was the unit used to measure turbocharger inlet pressure. However, the inHG unit is still used today in car performance modification to measure the amount of vacuum within the engine's intake manifold. This can be seen on Boost/Vacuum gauges.

In older literature, an inch of mercury based on the height of a column at 60 °F (15.6 °C) was common. :1 inHg_60 °F = 3,376.85 Pa

In English units: 1 inHg = 0.491098 psi, or 2.036254 inHg = 1 psi.

See also

References

Category:Units of pressure