Density Altitude Calculator
Calculate density altitude from field elevation, altimeter setting (QNH), and outside air temperature. Essential for performance calculations.
Results
What is it?
Density altitude is the altitude in the International Standard Atmosphere (ISA) that corresponds to the actual air density at your location. High density altitude means thinner air, which reduces engine power, propeller/rotor efficiency, and aerodynamic lift. Hot, high, and humid conditions create high density altitude and are the most dangerous for aircraft performance.
How to use
1. Enter your airport field elevation in feet. 2. Enter the current QNH (altimeter setting) in hPa (standard = 1013 hPa). 3. Enter the outside air temperature in degrees C. 4. The calculator shows density altitude, pressure altitude, and the ISA standard temperature at that pressure altitude.
Example scenario
Departing a mountain airport at 5,500 ft on a hot day (OAT = 35 C) with QNH = 1005 hPa. Pressure altitude = 5,500 + 30 x (1013 - 1005) = 5,740 ft. ISA temp at 5,740 ft = 3.5 C. Density altitude = 5,740 + 120 x (35 - 3.5) = 9,520 ft. Your aircraft performs as if it were at 9,520 ft on a standard day.
Pro tip
As a rule of thumb, density altitude increases approximately 120 ft for every 1 C above ISA. At density altitudes above 8,000 ft, most normally-aspirated piston engines lose 3-4% power per 1,000 ft, and takeoff roll can double compared to sea-level performance.