What is the difference between the 4 main types of altitudes? True, Absolute, Pressure, and Density Altitudes. True Altitude is the aircraft’s height above sea level. Absolute Altitude is the aircraft’s height above the terrain. Pressure Altitude is the aircraft’s height above the standard datum plane, or what is shown on the aircraft’s altimeter when it’s dialed to 29.92 (standard pressure). Density Altitude is pressure alt corrected for non-standard temperature. Since pressure in the air will