Density Altitude Calculator

How it works

Density altitude is pressure altitude corrected for temperature. Three steps:

1. Pressure altitude = field elevation + (29.92 − altimeter) × 1,000
2. ISA temperature at that altitude = 15 °C − 1.98 °C per 1,000 ft
3. Density altitude follows from the density ratio σ = δ / θ, inverted against the ISA density profile

The familiar rule of thumb — add about 120 ft per °C above ISA — is shown alongside so you can see how close it is. It is good to within a couple of hundred feet across normal conditions, which is why it survives.

Worked example

A field at 5,000 ft, altimeter 29.92, air temperature 30 °C. Pressure altitude is 5,000 ft. ISA there is about 5 °C, so you are 25 °C hot, and density altitude comes out near 8,000 ft. Your aircraft climbs, accelerates and stops like it is at 8,000 ft — on a runway that is only 5,000 ft up.

Why it bites

Takeoff roll and climb rate both degrade, and they degrade together, which is what makes hot-and-high accidents so consistent. Density altitude also rises with humidity — water vapor is lighter than dry air — and that effect is not in this calculation or in most POH charts. On a hot, humid day treat the number as optimistic.