Density Altitude Calculator
Enter the field elevation, altimeter setting and temperature to get the density altitude, the pressure altitude and the effect of humidity from an optional dew point.
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The density altitude calculator returns the altitude your aircraft performs at, after correcting the field elevation for pressure and temperature. Enter the field elevation, the altimeter setting and the outside air temperature, and the result gives the density altitude in feet, the pressure altitude, the air density and the density ratio.
Density altitude is the number that matters for takeoff, climb and engine power. Hot air, high elevation, low pressure and humid air all raise it. On a 5,000 ft field at 30 °C with an altimeter setting of 29.92 inHg, the calculator gives 7,802 ft, so the aircraft performs as it would at that higher altitude. Use the result as a planning aid and check the aircraft flight manual for the performance data.
How to use the density altitude calculator
- Enter the Field elevation in feet or meters, using its unit selector. The model runs from -1,500 ft to 20,000 ft.
- Enter the Altimeter setting in inHg or hPa (mb). Use the QNH from ATIS, METAR or the tower. A2992 is 29.92 inHg, and Q1013 is 1013 hPa.
- Enter the Outside air temperature in °C or °F.
- Open More options and enter the Dew point (optional) in the same unit as the temperature. It cannot be higher than the temperature. Leave it empty for dry air.
- Read the headline Density altitude, then the Pressure altitude and the Rule of thumb: PA + 120 x deviation line.
- Check the warning if one shows. It appears when the air is warmer than standard, and when the rule of thumb is more than 150 ft from the exact value.
- Open How it was calculated to see each step with your numbers.
Preset buttons load a standard day at sea level, a hot day at 5,000 ft, a hot and humid day, a cold day at a high field or a metric example. Copy link gives you a link to your entries, Print / save result prints or saves the result, and Reset restores the example values. The table under the result shows density altitude for other field elevations and temperatures at the same altimeter setting.
How do you calculate density altitude?
The calculator finds pressure altitude from the field elevation and altimeter setting, then compares the outside air temperature with the standard temperature at that altitude. It is the altitude in the standard atmosphere with the same air density as your field.
Pressure altitude follows the standard atmosphere pressure law, not the 1,000 ft per inHg shortcut. Example A (field 5,000 ft, 29.92 inHg, 30 °C, dry air) gives a pressure altitude of 5,001 ft and a density altitude of 7,802 ft.
What is the 120 in the density altitude formula?
The 120 is 120 feet of density altitude for each degree Celsius that the air is warmer than standard. The rule of thumb, PA + 120 x deviation, approximates the exact value, and the calculator shows both side by side.
At sea level one degree Celsius is worth 118 ft, close to 120. In example A the rule gives 7,990 ft, which is 188 ft above the exact 7,802 ft. It is a widely taught approximation; the FAA handbook text we checked does not state it.
How does humidity change density altitude?
Humidity raises density altitude because water vapor is lighter than dry air, so moist air is less dense. Enter a dew point and the Effect of humidity line shows the change. In example B, dry-air density altitude is 3,625 ft and the humid value is 4,063 ft, an increase of 437 ft.
The rule of thumb has no humidity term, so in example B it reads 287 ft below the exact value. The FAA handbook gives no humidity rule, but says humidity must be considered.
What does a high density altitude do to performance?
An aircraft performs as though it were at its density altitude. On takeoff the same indicated airspeed gives a greater true airspeed, and an unsupercharged piston engine loses power right away. On landing the greater true airspeed means a longer ground distance.
The FAA handbook example has a pressure altitude of 5,000 ft and 20 °C above standard. Its density level is above 7,000 ft, and the ground run may be closer to 1,000 ft than the 790 ft at standard temperature. This calculator gives 7,272 ft for the same inputs. The table under the result shows a 5,000 ft field at 29.92 inHg, rounded to 10 ft:
| Field 5,000 ft | -10 °C | 0 °C | 10 °C | 20 °C | 30 °C | 40 °C |
|---|---|---|---|---|---|---|
| Density altitude (ft) | 3,150 | 4,390 | 5,580 | 6,710 | 7,800 | 8,850 |
Sources
FAA-H-8083-25B Pilot’s Handbook of Aeronautical Knowledge (2016), chapter 11; FAA Aeronautical Information Manual, chapter 7 section 1 (AWOS density altitude remark); U.S. Standard Atmosphere 1976 (NASA-TM-X-74335), constants and Table I; Buck (1996) saturation vapor pressure, Buck Research CR-1A manual appendix 1; NIST SP 811 unit conversions. Checked October 2026.
Questions from readers
Where can I find density altitude online?
This calculator gives it from the field elevation, the altimeter setting and the temperature. The FAA Aeronautical Information Manual, chapter 7 section 1, says an AWOS reports density altitude in its remarks when it exceeds the field elevation by more than 1,000 ft.
What is the air density at 6,000 feet above sea level?
Standard air at 6,000 ft has a density of 1.024 kg/m3, which is a density ratio of 0.836.
Do I need the dew point?
No. Leave Dew point (optional) empty to get the dry-air result. Weather reports include the dew point, and entering it adds the effect of humidity.
Is density altitude the same as the altitude on my altimeter?
No. An altimeter set to 29.92 inHg reads pressure altitude, and density altitude adds the correction for temperature.
Which altimeter setting do I enter?
Enter the QNH from ATIS, METAR or the tower. A METAR group A2992 means 29.92 inHg, and Q1013 means 1013 hPa.
Can density altitude be lower than the field elevation?
Yes. In example C, a field at 6,000 ft with an altimeter setting of 30.30 inHg and -15 °C gives a density altitude of 3,341 ft, about 2,700 ft below the field.
Why does the rule of thumb differ from the exact value?
The rule of thumb is a straight-line approximation of the density calculation and has no humidity term. It reads 188 ft high in example A and 287 ft low in example B.
How does high density altitude affect flight?
High density altitude means the air is thinner, so the engine makes less power and the wings and propeller produce less lift and thrust. Takeoff roll gets longer, climb rate drops, and true airspeed is higher for the same indicated airspeed. Check the aircraft flight manual charts for the actual numbers.
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