Density altitude calculator
Density altitude is the altitude the aircraft thinks it is at. On a hot day at a high field it can be thousands of feet above the ground you are standing on.
ft
hPa
degrees C
Density altitude
3635ft
- Pressure altitude
- 1500 ft
- Deviation from ISA
- 18.0 degrees C
- Air density
- 1.0937 kg/m3
- Density relative to sea level
- 0.8928
- Take-off roll multiplier Roughly how much longer the ground roll becomes.
- 1.185
- Climb rate multiplier
- 0.893
- ISA temperature at that altitude
- 12.0 degrees C
Show the working
- Field elevation = 1500
- Altimeter setting = 1013.25
- Temperature = 30
- Dew point = 18
- Pressure altitude = 1500 + (1013.25 - 1013.25) * 27 = 1500
- ISA temperature at that altitude = 15 - 1.98 * 1500 / 1000 = 12.03
- Deviation from ISA = 30 - 12.03 = 17.97
- Density altitude = 1500 + 118.8 * 17.97 = 3634.84
- vapour_pressure = 6.11 * 10^(7.5 * 18 / (237.7 + 18)) = 20.6065
- station_pressure = 1013.25 * (1 - 2.25577e-5 * 1500 * 0.3048)^5.25588 = 959.518
- Air density = (959.518*100 - 20.6065*100)/(287.058*(30+273.15)) + 20.6065*100/(461.495*(30+273.15)) = 1.093 67
- Density relative to sea level = 1.093 67 / 1.225 = 0.892 791
- Take-off roll multiplier = 0.892 791 > 0 ? 1 / 0.892 791^1.5 : 0 = 1.185 43
- Climb rate multiplier = 0.892 791 = 0.892 791
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- pressure altitude = elevation + (1013.25 - QNH) x 27 feet per hPa
- density altitude = pressure altitude + 118.8 x (OAT - ISA temperature)
- ISA lapse rate is 1.98 degrees Celsius per 1000 feet
Take-off distance grows roughly with the inverse 1.5 power of density ratio, and climb rate falls roughly in proportion to it.
Humidity lowers density a little further, which the air density figure here accounts for but the standard density altitude formula does not.
This is a planning and study tool. Use certified charts, an approved flight manual and official publications for anything operational.