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# Converting Millibars to Millimeters of Mercury

## Worked Pressure Unit Conversion Problem

This example problem demonstrates how to convert the pressure unit millibar (mbar) to millimeters of mercury (mm Hg). Millimeters of mercury is a pressure measurement usually associated with barometers and common in meteorology. A glass tube is sealed at one end and the open end is submerged into a pool of liquid mercury. Differences in air pressure on the mercury causes the level of the mercury to rise and fall inside the glass tube. The differences in height are measured in millimeters, which explains the name "millimeters of mercury". The bar is a pressure unit defined as 100 kilopascals and 1 millibar is 1/1000 bar.

Problem:

The average air pressure at sea level is 1010 mbar. What is this pressure in mm Hg?

Solution:

1 mbar = 0.75218 mm Hg

Set up the conversion so the desired unit will be cancelled out. In this case, we want mm Hg to be the remaining unit.

pressure in mm Hg = (pressure in mbar) x (0.75218 mm Hg/1 mbar)
pressure in mm Hg = (1010 x 0.75218) mm Hg
pressure in mm Hg = 760 mm Hg

The average sea level air pressure is 760 mm Hg.
##### Chemistry Homework Resources

Anne Marie Helmenstine, Ph.D.