Hectopascal

The hectopascal is a unit of pressure in the SI system, equal to 100 pascals. Its symbol is hPa. It is commonly used in meteorology and aviation to report atmospheric pressure. The hectopascal is one of the non-SI units accepted for use with SI.

It is equivalent to the millibar (mb); 1 hPa = 1 mb. At sea level, standard atmospheric pressure is about 1013.25 hPa (or mb), equal to 101325 Pa. In terms of bar, 1 bar = 1000 hPa. The unit arises from the decimal prefix 'hecto-' and the pascal unit.

It is widely used on weather forecasts, weather maps, pressure readings in meteorological stations worldwide. Many maritime and aviation contexts prefer hPa to reflect pressure in thousands of pascals. Some older literature uses mb, but modern conventions often prefer hPa.

The pascal is the SI base unit of pressure; hPa is not an SI unit but is accepted for use with the SI. It is useful for human-scale pressure values; the range around 1000 hPa is common for atmospheric pressure.