How is pressure altitude calculated?

Pressure altitude is determined by using the current altimeter setting. This measurement is based on the standard atmospheric pressure and allows pilots to understand their altitude in relation to the pressure environment at sea level. The standard pressure is set at 29.92 inches of mercury (inHg) or 1013.25 hPa.

When a pilot adjusts the altimeter to the local barometric pressure (the current altimeter setting), it allows for accurate altitude readings, accounting for variations in atmospheric pressure due to weather conditions. This is essential for maintaining proper altitude, especially in situations where pressure changes can significantly affect flight safety and aircraft performance.

In contrast, calculating pressure altitude using aircraft weight or converting altitude into airspeed does not accurately define the pressure altitude. Similarly, subtracting pressure from a fixed value does not reflect the necessary adjustments based on local atmospheric conditions or provide a reliable method for determining pressure altitude. Thus, using the current altimeter setting is the standard practice for calculating pressure altitude.