hectopascals

A hectopascal, symbol hPa, is a unit of pressure in the metric system. It equals 100 pascals (Pa). The prefix hecto denotes a factor of 100, so 1 hPa = 100 Pa. In meteorology and aviation, hPa is commonly used to report atmospheric pressure at sea level and at altitudes, and it is effectively equivalent to the millibar (mb).

Although the pascal is the SI base unit for pressure, the hectopascal remains widely used for weather reports because atmospheric pressures typically fall in the hundreds of hectopascals. For example, standard sea-level pressure is about 1013.25 hPa (101325 Pa). Typical surface-pressure ranges are roughly 970–1050 hPa, with strong weather systems sometimes extending beyond these values.

Conversions and relationships: 1 hPa = 100 Pa; 1 kPa = 10 hPa; 1 bar = 1000 hPa. In meteorological data, values are frequently given in hPa, but pressure can also be reported in pascals or kilopascals depending on the context.

Notes on usage: The hectopascal is an SI-accepted unit for pressure used with the SI framework, but it is a non-SI unit in strict terms. The term remains standard in weather and aviation, where it provides a convenient scale for typical atmospheric pressures.