Updated November 2026 · free, works in your browser
Show the formula
Density altitude is the altitude the aircraft "feels" in terms of air density: field elevation corrected for non-standard pressure and temperature. Enter the field elevation, the outside air temperature and the altimeter setting above to get pressure altitude and density altitude instantly. The higher the density altitude, the thinner the air, and the longer the takeoff roll and the weaker the climb.
How to use the density altitude calculator
- Enter the field elevation and choose feet or metres.
- Enter the outside air temperature and choose °C or °F.
- Enter the altimeter setting (QNH) from the latest weather report and choose inHg or hPa. The default 29.92 inHg is standard pressure.
- Read the density altitude, pressure altitude, ISA temperature and temperature deviation. The result updates as you type.
- Use the copy button to save a link that restores your inputs.
How it is calculated
The calculator uses the standard rule-of-thumb method taught in pilot training, based on the International Standard Atmosphere (ISA) and described in the FAA Pilot's Handbook of Aeronautical Knowledge.
- Pressure altitude = field elevation + (29.92 − altimeter setting in inHg) × 1,000 ft. Pressure altitude is the altitude shown when the altimeter is set to 29.92 inHg (1013.25 hPa).
- ISA temperature = 15 °C − 1.98 °C per 1,000 ft of pressure altitude. This is the temperature the standard atmosphere has at that level.
- Density altitude = pressure altitude + 120 ft × (outside air temperature − ISA temperature in °C).
Hectopascal values are converted at 33.8639 hPa per inHg, and metres at 0.3048 m per foot. The formula ignores humidity, which makes the air slightly less dense, so treat the result as a planning figure and use the aircraft's own performance charts for decisions.
What changes density altitude
| Change | Approximate effect on density altitude |
|---|---|
| Temperature 10 °C above ISA | About 1,200 ft higher |
| Temperature 20 °C above ISA | About 2,400 ft higher |
| Temperature 10 °C below ISA | About 1,200 ft lower |
| Altimeter setting 0.10 inHg lower | About 100 ft higher |
| Altimeter setting 0.10 inHg higher | About 100 ft lower |
As an example at 30 °C and 29.92 inHg, a field at 334 ft (Burlington) has a density altitude of about 2,213 ft, a field at 732 ft (Morrisville-Stowe) about 2,706 ft, and a field at 1,470 ft (Warren) about 3,619 ft.
Frequently asked questions
What is the difference between pressure altitude and density altitude?
Pressure altitude corrects the elevation for atmospheric pressure only. Density altitude then adds a correction for temperature, so it reflects the actual air density.
Why does density altitude matter for takeoff?
Thin air reduces engine power, propeller thrust and wing lift. At a high density altitude the aircraft needs more runway to lift off and climbs more slowly, even though the airspeed indicator reads normally.
Can density altitude be lower than field elevation?
Yes. On a cold day or with a high altimeter setting, the air is denser than standard and the density altitude can be below the field elevation.
How can I estimate density altitude without a calculator?
Find the pressure altitude, work out how many degrees the temperature is above or below ISA, and add or subtract 120 ft for each degree Celsius.
Does humidity change the result?
Humid air is slightly less dense than dry air, so real density altitude can be a little higher than shown. The standard method leaves humidity out.
If your flying trip takes you to a mountain field on a warm afternoon, plan generous margins: arrive the day before, fly in the cooler morning hours, and keep your schedule flexible in case weather or performance limits delay a departure. Booking a hotel close to the airfield for the night before and after makes that flexibility easy.
Other tools
- Crosswind Component CalculatorEnter the runway heading, wind direction and wind speed to get the crosswind and headwind or tailwind components.
- Wind Correction and Groundspeed CalculatorEnter course, true airspeed and wind to get the wind correction angle, heading to fly and groundspeed (the E6B wind problem).
- Airport Runway Length CheckerSearch a Vermont airport and see its longest runway, surface type and whether your required distance fits.
This is an independent guide. It is not affiliated with Vermont Agency of Transportation.