Millibar (mbar)

Metric (SI)Current unit

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

1 millibar = 100 pascals (exactly).

About the millibar

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.

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

Millibar conversion chart

1 millibar expressed in every other pressure unit:

More Metric (SI) units

• pascal (pressure)
• kilopascal (pressure)
• hectopascal (pressure)
• megapascal (pressure)
• gigapascal (pressure)
• bar (pressure)
• standard atmosphere (pressure)
• meter (length)
• kilometer (length)
• centimeter (length)
• millimeter (length)
• micrometer (length)
• nanometer (length)
• picometer (length)
• decimeter (length)
• hectometer (length)

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