What is pressure altitude?

Pressure altitude is the altitude in the International Standard Atmosphere (ISA) at which the pressure is equal to the atmospheric pressure at a given location. It is used in aviation to determine aircraft performance and is calculated by adjusting the indicated altitude for non-standard atmospheric pressure.

Pressure altitude is a measure of the mean sea level pressure of the atmosphere at a given point in the air. It is an altitude calculated by assuming that the atmospheric pressure at a given level is the same as the pressure at sea level. This allows for a more accurate representation of the altitude of an aircraft or the height of a mountain when compared to using the geometric altitude, which is the actual vertical distance above the Earth's surface.