Density altitude calculator
Pick an airport and see the density altitude and pressure altitude from the current METAR.
This ignores humidity. So does your POH. On a humid day the real density altitude is higher than either one says.
The formula
The altimeter setting is in hectopascals (1013.25 is standard sea level), and the temperature in degrees C. Standard temperature drops by about 2 °C per thousand feet. Every degree above standard adds 118.8 ft of density altitude.
At Centennial (5,885 ft) with 29.92 inHg and 31 °C:
That is a 56% longer ground roll than the field elevation alone suggests.
How this works
- Why the air matters more than the elevation
- An engine burns a mass of air per stroke, not a volume. At higher temperature or lower pressure, each cubic foot holds fewer molecules. The engine ingests less mass, produces less power, and runs rich on the sea-level mixture setting. The wings and propeller move through the same thinner air: less lift per unit area, less thrust per revolution. Density altitude puts a single number on all of that — the altitude in the standard atmosphere where the air is equally thin.
- What it means in practice
- A Cessna 172 at Centennial on a 31°C day needs 56% more ground roll than at sea level on a standard day. At Leadville (9,934 ft) on that same afternoon, density altitude can exceed 13,000 ft — higher than many non-turbocharged aircraft can sustain level flight. The POH performance charts use the same calculation shown above.
- Humidity is not included
- Water vapour displaces heavier nitrogen and oxygen, so humid air is less dense. The correction runs 100 to 400 ft on a hot, humid afternoon — exactly when the margin is thinnest. The error is always in the dangerous direction: real density altitude higher than calculated, aircraft performing worse than the numbers say. The standard formula omits it. So do POH charts. Both understate the hazard by the same amount, which is why the two agree and neither is safe.
Flying in high density altitude
Fly in the morning
Temperature drives density altitude more than pressure does. At many mountain airports the DA is 2,000 ft lower at sunrise than at 2 PM. Plan departure before the heat of the day.
Reduce weight
A lighter aircraft needs less lift and less runway. Leave nonessential weight behind. On a hot day at Leadville, every 100 lb you remove shortens the takeoff roll noticeably.
Lean the mixture for takeoff
At high elevation the engine runs rich on the sea-level mixture setting. Lean to peak RPM before takeoff per the POH. The power gain can be 10% or more.
Use the 50/70 rule
If you have not reached 70% of rotation speed by the 50% point of the runway, abort the takeoff. High DA stretches the acceleration phase, and this rule catches it early.
Expect a lower climb rate
Thin air reduces both engine power and propeller efficiency. A Cessna 172 that climbs at 700 fpm at sea level may manage 300 fpm at a density altitude of 8,000 ft. Plan for terrain clearance accordingly.
Notable high-elevation airports
At these airports, density altitude is a factor on most summer days. A hot afternoon at Leadville can push the density altitude above 13,000 ft. Even Denver reaches 8,000 ft on a warm day with low pressure.
| Airport | ICAO | Elevation | Note |
|---|---|---|---|
| Leadville, Colorado | KLXV | 9,934 ft | Highest airport in the contiguous US |
| Telluride, Colorado | KTEX | 9,070 ft | Steep terrain on all sides |
| Granby, Colorado | KGNB | 8,203 ft | Hot summer afternoons push DA above 12,000 ft |
| Angel Fire, New Mexico | KAXX | 8,382 ft | High desert, low humidity |
| Santa Fe, New Mexico | KSAF | 6,348 ft | Summer heat routinely adds 3,000 ft of DA |
| Centennial, Colorado | KAPA | 5,885 ft | Busiest GA field in Colorado |
| Denver, Colorado | KDEN | 5,431 ft | Highest major hub in the US |
| Albuquerque, New Mexico | KABQ | 5,355 ft | Hot desert summers |
| Prescott, Arizona | KPRC | 5,045 ft | Major flight training location |
| Flagstaff, Arizona | KFLG | 7,014 ft | Elevation surprises pilots expecting desert conditions |
Frequently asked questions
- What is density altitude?
- Density altitude is the altitude at which the current air density matches standard atmospheric conditions. On a hot day at a high field, the air is thinner than the elevation suggests. The engine produces less power, the wings generate less lift, and the propeller moves less air. The aircraft performs as if it were at a higher airport.
- How do I calculate density altitude?
- Start with pressure altitude: subtract the current altimeter setting from the standard 29.92 inHg, multiply by 1,000, and add the field elevation. Then apply the ISA deviation: each degree Celsius above standard temperature adds about 120 ft of density altitude. Each degree below standard subtracts about 120 ft.
- What is pressure altitude?
- Pressure altitude is the altitude the altimeter reads when you set it to 29.92 inHg (1013.25 hPa). It removes local pressure variations and gives a consistent reference. Above 18,000 ft in the US, all aircraft fly on pressure altitude (flight levels) so that vertical separation uses the same reference.
- What is ISA deviation?
- ISA deviation is the difference between the actual temperature and the standard temperature at a given pressure altitude. The International Standard Atmosphere (ISA) defines standard temperature as 15°C at sea level, decreasing by about 2°C per 1,000 ft. A positive deviation means the air is warmer and less dense than standard.
- Why is density altitude dangerous?
- High density altitude increases takeoff distance, reduces climb rate, and lowers engine power. A pilot who plans for field elevation alone may run out of runway. The classic accident scenario is a hot afternoon at a high-altitude airport with a heavy aircraft. The POH performance charts use density altitude, not field elevation.
- Does humidity affect density altitude?
- Yes. Water vapour is lighter than the nitrogen and oxygen it displaces, so humid air is less dense. The standard formula ignores humidity, and so do most POH charts. The vapor pressure correction adds roughly 100 to 400 ft of density altitude on a hot, humid day. The error always works against the pilot: the real density altitude is higher than calculated, so the aircraft performs worse than the numbers suggest.
- What is a safe density altitude for takeoff?
- There is no universal number. The safe threshold depends on the aircraft, its weight, the runway length, and obstacles. Check the takeoff distance in the POH for the current density altitude and weight, then compare it to the available runway. Add a safety margin for gusts and surface conditions.
Not a substitute for an official pre-flight weather briefing.