Inch of mercury

Inch of mercury (inHg and ″Hg) is a non-SI unit of measurement for pressure. It is used for barometric pressure in weather reports, refrigeration and aviation in the United States.

Inch of mercury
Early American barometer calibrated in inches of mercury
General information
Unit ofPressure
1 inHg in ...... is equal to ...
   SI units   3.38639 kPa
   United States customary units   0.491154 psi

It is the pressure exerted by a column of mercury 1 inch (25.4 mm) in height at the standard acceleration of gravity. Conversion to metric units depends on the temperature of mercury, and hence its density; typical conversion factors are:[1]

Conditions Pressure
conventional 3386.389 pascals
32 °F (0 °C) 3386.38 pascals
60 °F (16 °C) 3376.85 pascals

In older literature, an "inch of mercury" is based on the height of a column of mercury at 60 °F (15.6 °C).[1]

1 inHg60 °F = 3,376.85 pascals (33.7685 hPa)

In Imperial units: 1 inHg60 °F = 0.489 771 psi, or 2.041 771 inHg60 °F = 1 psi.

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