Density Altitude Calculator
The aircraft flies the air it is in, not the altimeter.
Work out Density Altitude. The aircraft flies the air it is in, not the altimeter. Shows the working, not just the answer.
Density altitude
4,252 ft
Pressure altitude 2,000 ft · ISA +19 °C
The aircraft flies the density altitude and ignores everything else. A hot day at a low airfield performs like a cold day thousands of feet higher, and the altimeter shows none of it — which is why performance surprises happen on exactly the days that feel pleasant. Each degree above standard adds roughly 119 ft of density altitude. A 30 °C day at a 2,000 ft field is already past 4,000 ft, and that is before humidity, which lowers density further because water vapour is lighter than air. Performance factors here are indicative. Use the aircraft's own charts for anything that matters — they account for the specific aeroplane, surface, slope and technique in ways no general rule can.
How the Density Altitude Calculator works
Pressure and density altitude from field elevation, altimeter setting and temperature, with humidity counted and the takeoff and climb penalties spelt out. A hot day at a low field performs like a much higher one.
Also known as: what is my density altitude · hot and high performance penalty · pressure altitude from qnh · isa deviation calculator
Frequently asked questions
What is density altitude?
The altitude at which the standard atmosphere has the density you are actually flying in. The aircraft's performance depends on it and on nothing else — the altimeter shows none of it.
How do you calculate density altitude?
Pressure altitude plus about 119 ft for every degree Celsius above the ISA temperature for that pressure altitude. ISA is 15 °C at sea level, lapsing 1.98 °C per 1,000 ft.
How much does heat matter?
Enormously. A 30 °C day at a 2,000 ft field puts density altitude past 4,000 ft before humidity is counted, and takeoff roll grows faster than linearly with it.
Does humidity affect density altitude?
Yes, and in the direction that surprises people: moist air is lighter than dry air, because water vapour is lighter than the nitrogen and oxygen it displaces.
What is pressure altitude?
What the altimeter reads with 1013.25 hPa set — field elevation corrected for the pressure setting at roughly 27 ft per hPa. It is the input to density altitude, not the answer.
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