Hectopascals to Millibars (hPa to mbar)

1 hectopascal equals 1 millibar exactly.

How to convert hectopascals to millibars

To convert hectopascals to millibars, multiply the number of hectopascals by 1. This factor is exact. To go the other way, multiply millibars by 1.

millibars = hectopascals × 1

Example: 10 hectopascals = 10 millibars.

About these units

Hectopascal (hPa)

Metric (SI)Current unit

100 pascals, equal to one millibar. The standard unit in weather forecasts and barometers.

Weather forecasters rarely think in pascals, and the hectopascal exists largely to avoid changing their numbers. When SI arrived, meteorologists generally switched from the millibar to the hectopascal, which equals exactly 100 Pa and exactly one millibar, so existing readings carried over unchanged. Observations are typically reported in hPa, following the World Meteorological Organization recommendation, though many scientific fields dislike the hecto prefix because they prefer steps of 1,000.

A typical sea-level reading is about 1,013 hPa. The lowest non-tornadic pressure ever measured was 870 hPa, in Typhoon Tip on 12 October 1979, and the highest sea-level pressure, 1,084.8 hPa, came at Tosontsengel, Mongolia, on 19 December 2001, at a station above 750 meters. At low altitudes, pressure drops about 12 hPa for every 100 meters you climb.

Aviation weather reports, such as the QNH in a METAR, use hectopascals or millibars in most countries, while the US, Canada and Japan quote altimeter settings in inches of mercury.

1 hectopascal = 100 pascals (exactly).

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

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.