What is density altitude?
Density altitude is pressure altitude corrected for non-standard temperature: the altitude in the standard atmosphere at which the air density equals the density you have right now. Hot, high and humid conditions raise density altitude, so the engine makes less power, the propeller and wing produce less thrust and lift, and takeoff and climb performance degrade — a leading factor in high-terrain accidents (FAA Pilot's Handbook, FAA-H-8083-25C, Ch. 11).
The ISA and the working formula
The ICAO Standard Atmosphere fixes sea level at 15 °C and 1013.25 hPa with a temperature lapse of about 2 °C per 1000 ft (6.5 °C/km) up to 11 km. Pressure altitude comes from the altimeter setting; a widely used field approximation is DA ≈ PA + 120 × (OAT − ISA temp), where the ISA temperature at pressure altitude is 15 − 2 × (PA/1000) °C. This tool uses the full barometric relation, not just the rule of thumb.
How to use the calculator
Enter elevation, altimeter setting and temperature. The tool first converts to pressure altitude, then applies the temperature (and optional humidity) correction to get density altitude, and reports the deviation from standard so you can anticipate reduced climb rate and longer ground roll.
Note: humidity lowers air density (water vapor is lighter than dry air), so a dew-point correction raises density altitude slightly; most performance charts ignore it, but it matters on hot, humid days. Always cross-check against your aircraft's performance charts (NOAA/NWS density altitude reference, NOAA/NWS).
Frequently asked questions
What is density altitude?
Density altitude is pressure altitude corrected for temperature: the altitude in the standard atmosphere where the air density matches your current density. High density altitude means thinner air and degraded aircraft performance.
How do you calculate density altitude?
First convert your altimeter setting and elevation to pressure altitude, then correct for temperature. A common field rule is DA = PA + 120 x (OAT - ISA temperature), where ISA temperature = 15 - 2 x (PA/1000) degrees C.
Why does density altitude matter for aircraft?
Engine power, propeller thrust and wing lift all depend on air density. A high density altitude reduces all three, lengthening the takeoff roll, lowering the climb rate and raising the true airspeed for a given indicated airspeed.
Does humidity affect density altitude?
Yes. Water vapor is less dense than dry air, so higher humidity lowers air density and raises density altitude. The effect is small compared with temperature and altitude but is noticeable on hot, humid days.
References
- U.S. Federal Aviation Administration, Pilot's Handbook of Aeronautical Knowledge, FAA-H-8083-25C (2023), Ch. 11 (Aircraft Performance).
- International Civil Aviation Organization, Manual of the ICAO Standard Atmosphere, Doc 7488, 3rd ed. (1993) — sea-level 15 °C, 1013.25 hPa, lapse rate 6.5 °C/km.
- NOAA / U.S. National Weather Service, density altitude calculator and equations (NOAA/NWS).