Inch Of Mercury (inHg)

US & ImperialCurrent unit

About 3,386.39 pascals. US weather reports and aircraft altimeters quote barometric pressure in inches of mercury.

1 inch of mercury = 3,386.38864 pascals (approximately).

About the inch of mercury

Barometers in the United States still speak in inches. The inch of mercury is the pressure exerted by a 1-inch (25.4 mm) column of mercury under standard gravity, which is a conventional value of about 3,386.389 pascals. Because mercury's density depends on temperature, older literature that used a 60 degrees Fahrenheit basis gives about 3,376.85 pascals instead.

Its modern home is weather and flying. US weather reports quote barometric pressure in inHg, and North America and Japan give altimeter settings in it. Aircraft at higher altitudes set their altimeters to a standard 29.92 inHg, which is where flight levels come from, and that number equals one standard atmosphere.

Mechanics know it from vacuum and boost gauges. Technicians describe refrigerant-system vacuum in inHg, automotive cooling system fill tools typically hold 22 to 27 inHg of vacuum, and railways once used it for vacuum brakes.

Sources: Wikipedia: Inch of mercury; Wikipedia: Standard atmosphere (unit); Wikipedia: Atmospheric pressure

Inch Of Mercury conversion chart

1 inch of mercury expressed in every other pressure unit:

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