What does pressure altitude refer to?

Pressure altitude refers to the vertical distance above the standard datum plane, which is based on a standard atmospheric pressure, typically defined as 29.92 inches of mercury (Hg) at sea level. This measurement is essential for aircraft performance calculations and is utilized in various aspects of aviation, including flight planning and altitude assignments. By using the standard datum plane, pressure altitude provides a consistent reference point for determining altitude regardless of local atmospheric variations that might exist due to temperature, humidity, or barometric pressure changes.

In aviation, pilots need this standardized measurement to ensure safe operation and navigation, especially when flying at higher altitudes where variations in atmospheric conditions can greatly affect aircraft performance.