Millimeters Of Mercury to Millibars (mmHg to mbar)

1 millimeter of mercury equals 1.333223874 millibars (rounded).

How to convert millimeters of mercury to millibars

To convert millimeters of mercury to millibars, multiply the number of millimeters of mercury by 1.333223874. The factor is rounded to 10 significant digits. To go the other way, multiply millibars by 0.7500615758 (rounded).

millibars = millimeters of mercury × 1.333223874

Example: 10 millimeters of mercury = 13.33223874 millibars.

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

Millibar (mbar)

Metric (SI)Current unit

One thousandth of a bar, equal to one hectopascal. Standard atmospheric pressure is 1,013.25 mbar.

Millibar and hectopascal are the same pressure with different pedigrees. The millibar was introduced alongside the bar by Vilhelm Bjerknes, and meteorologists worldwide adopted it because the values are convenient: a thousandth of a bar puts ordinary air pressure near 1,000. Standard atmospheric pressure is 1,013.25 millibars.

When SI came in, some meteorologists switched to hectopascals, which carry exactly the same numbers. The millibar did not vanish, though. The symbol mb is still common, and Americans know the unit from US hurricane and cyclone reports.

A few readings give the scale. The record-low non-tornadic pressure of 870 hPa in Typhoon Tip in 1979 equals 870 millibars, and falling pressure of about 12 hPa per 100 meters of altitude means a mountain road can shave tens of millibars off a barometer reading in a short climb.

1 millibar = 100 pascals (exactly).

Sources: Wikipedia: Bar (unit); Wikipedia: Hectopascal; Wikipedia: Atmospheric pressure

Related conversions

See all pressure units.