Millimeters Of Mercury to Inches Of Mercury (mmHg to inHg)

1 millimeter of mercury equals 0.03937007874 inches of mercury (rounded).

1 millimeter of mercury = 0.03937007874 inches of mercury

How to convert millimeters of mercury to inches of mercury

To convert millimeters of mercury to inches of mercury, multiply the number of millimeters of mercury by 0.03937007874. The factor is rounded to 10 significant digits. To go the other way, multiply inches of mercury by 25.4.

inches of mercury = millimeters of mercury × 0.03937007874

Example: 10 millimeters of mercury = 0.3937007874 inches of mercury.

About these units

Millimeter Of Mercury (mmHg)

ScientificCurrent unit

About 133.322 pascals, the pressure from a 1 mm column of mercury. Blood pressure is still reported in mmHg.

Where the torr honors a person, the millimeter of mercury describes a gauge. It is a manometric unit: originally the pressure from a mercury column 1 mm tall, which means it depends on an assumed fluid density and on gravity. Mercury manometers were among the first accurate pressure gauges, and 17th-century experiments by Torricelli and then Pascal, whose mercury stood at about 23 inches on a mountaintop against about 26 at its base, showed that air has weight and that pressure drops with altitude.

To remove the ambiguity, mmHg is now fixed at exactly 133.322387415 Pa, using a conventional mercury density of 13,595.1 kg per cubic meter and standard gravity. The torr, defined as one 760th of a standard atmosphere, differs from it by only about 0.000015 percent.

Mercury is toxic and its readings vary with temperature and local gravity, so mercury gauges are now used less, and the unit's use is discouraged. Medicine nonetheless keeps it, especially for blood pressure, which is reported relative to atmospheric pressure, and hypertension guidelines in the US and Europe still use it.

1 millimeter of mercury = 133.3223874 pascals (approximately).

Sources: Wikipedia: Millimetre of mercury; Wikipedia: Torr; Wikipedia: Blaise Pascal

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.

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.

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

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

Related conversions

See all pressure units.