Density Altitude

Density altitude is the equivalent pressure altitude of a standard atmosphere because of temperature changes.

The density of the air decreases as the temperature increases. The air acts as though it was at a higher pressure altitude.

Pressure altitude is what an airplane's altimeter would read when set to 29.92.

Example 1.
Suppose the temperature was 18 degrees F at a pressure altitude of 9,500 ft. From the chart below, the density altitude is 9,000 ft.

Example 2.
Suppose the temperature was 97 degrees F at a pressure altitude of 4,950 feet. From the chart below, the density altitude is 8,200 ft.