3. Atmospheric pressure

Atmospheric pressure in the International System of Units (SI) is defined as the force exerted by the weight of air (or more generally, a gas mixture) on a given surface, divided by that surface area.

The base unit of pressure in the SI system is the pascal (Pa), where 1 Pa = 1 newton per square meter (N/m ² ).

The unit of pressure used in meteorology is the hectopascal (hPa), but many barometers are still calibrated in other units.

The main conversion factors are: