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Density Altitude Calculator

Enter your pressure altitude and outside air temperature to find density altitude.

Result

7,988 ft
5.1 °C
24.9 °C

How it is calculated

Step 1, ISA temperature at your altitude: ISA = 15 − 1.98 × (PA ÷ 1000) in °C, where PA is pressure altitude in feet. Step 2, density altitude: DA = PA + 120 × (OAT − ISA), where OAT is the outside air temperature in °C. The deviation shown is OAT − ISA. The 120 ft per degree is the common rule-of-thumb approximation, and the lapse rate is a flat 1.98 °C per 1,000 ft. The tool does not use humidity, and it asks for pressure altitude, not field elevation (see mistakes). Negative altitudes and temperatures are accepted. This is a standard-atmosphere calculation, so it does not depend on country, and its result is a planning estimate, not a performance chart.

Worked example

Pressure altitude 5000 ft, outside air temperature 30 °C. ISA = 15 − 1.98 × 5 = 5.1 °C. Deviation = 30 − 5.1 = 24.9 °C above standard. DA = 5000 + 120 × 24.9 = 5000 + 2988 = 7,988 ft. The aircraft performs as if it were at about 8,000 ft.

Try this example →

Common mistakes

  • Entering field elevation as pressure altitude. Pressure altitude is read with 29.92 inHg set on the altimeter; when the altimeter setting is above or below that, the two differ.
  • Entering the temperature in Fahrenheit; the input is degrees Celsius.
  • Expecting humidity to change the answer. This formula ignores it, so a muggy day can be worse than the displayed value.
  • Confusing the deviation with the temperature itself: 24.9 °C is how far above ISA the day is, not the air temperature.
  • Treating the result as an aircraft performance figure. It is only the altitude to look up in the aircraft's own charts.

About this calculator

Density altitude is pressure altitude corrected for non-standard temperature — the altitude in the International Standard Atmosphere (ISA) at which the air would have the same density as the air you're actually flying in. It's found by taking pressure altitude and adjusting it upward roughly 120 feet for every degree Celsius the outside air temperature is above the ISA standard temperature for that altitude (and downward for colder-than-standard air), since ISA temperature itself drops about 2°C per 1,000 feet from a 15°C sea-level baseline.

Hot, humid, high-elevation days push density altitude well above field elevation, which thins the air enough to lengthen takeoff roll, reduce climb rate, and cut engine and propeller performance. Pilots, flight instructors, and dispatchers check density altitude before departure from high or hot airports to confirm runway length and payload are safe for the day's conditions.

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Comments (1)

  • Editorial team

    Run it twice for the same airfield, once with the cool morning temperature and once with the afternoon high. By this formula every 10 degrees Celsius of extra heat adds about 1,200 feet of density altitude, which is why hot afternoons at high airfields feel so different from early flights. Take the final number to the aircraft's own performance charts. What pressure altitude and temperatures are you planning around?

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