Hectopascal (hPa)

Metric (SI)Current unit

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

1 hectopascal = 100 pascals (exactly).

About the hectopascal

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.

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

Hectopascal conversion chart

1 hectopascal expressed in every other pressure unit:

More Metric (SI) units

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

All Metric (SI) units

Browse all pressure units.