How this calculator works
Density altitude is the height in the standard atmosphere with the same air density as the entered state. Moist-air density is computed from component partial pressures, then the ISA density profile is inverted through 20 km. Altimeter settings are reduced using the same standard pressure profile. The chart varies temperature at fixed pressure; dew-point mode holds vapour pressure fixed while RH mode holds relative humidity fixed. These are different scenarios. Aircraft performance also depends on aircraft configuration and its approved performance data.
Formula
rho = (p-e)/(R_d T)+e/(R_v T). Find h for rho_ISA(h)=rho. For h<=11 km: rho_ISA = rho0 (1-Lh/T0)^[g/(R L)-1]; above 11 km density decays exponentially.
Worked example
For dry air at 15 C and 101325 Pa, density is about 1.22505 kg/m3 and density altitude is close to sea level. The small offset reflects the published gas-constant approximations used for moist air and ISA.
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Frequently asked questions
Why does hot weather raise density altitude?
Warmer air is less dense at the same pressure, matching a higher point in the standard atmosphere.
Does humidity matter?
Yes. Humid air is slightly less dense at the same pressure and temperature.
Is this station elevation?
No. Density altitude is a comparison with a reference atmosphere and can differ substantially from actual elevation.