Pressure altitude is the height above a standard reference point, typically sea level, where the atmospheric pressure is equal to 29.92 inches of mercury (Hg) or 1013.25 hPa. It is used in aviation to ensure consistent altitude readings, regardless of local weather conditions. Pilots use pressure altitude to determine aircraft performance and safety. Changes in atmospheric pressure due to weather can affect true altitude, so pressure altitude provides a standardized way to measure height. This is crucial for maintaining safe separation between aircraft in flight, especially in crowded airspace.