Density Altitude Calculator
Calculate density altitude from field elevation, altimeter setting, outside air temperature, and optional dewpoint. Density altitude represents the altitude at which the aircraft "thinks" it is operating, directly affecting engine power output, propeller efficiency, and aerodynamic lift.
Worked Example
An airport at 5,000 ft MSL with an altimeter of 29.72 inHg and OAT of 35°C:
- PA = 5,000 + (29.92 − 29.72) × 1,000 = 5,200 ft
- ISA at 5,200 ft = 15 − (5.2 × 1.98) = 4.7°C
- ISA Deviation = 35 − 4.7 = +30.3°C
- DA ≈ 5,200 + (120 × 30.3) = 8,836 ft
Why This Matters to Pilots
Density altitude is the single most important performance factor. On a hot day at a high-elevation airport, density altitude can exceed the field elevation by thousands of feet, dramatically reducing takeoff performance, climb rate, and engine power.
The famous "high, hot, and humid" conditions at airports like Denver (5,431 ft) or Leadville (9,934 ft) can push density altitude well above 10,000 ft, meaning the aircraft performs as if it were at that altitude.
Always check density altitude before every flight and compare performance data to your aircraft's POH charts.
Limitations & Assumptions
- Uses the standard lapse rate (1.98°C/1000 ft) which is an average, not actual conditions.
- The 120-factor approximation is less accurate at extreme altitudes or temperatures.
- Humidity correction (when dewpoint is entered) uses a Magnus-type vapor pressure approximation and a virtual-temperature adjustment.
- On hot days the 120-factor rule can read a few hundred feet higher than an exact air-density calculation.
- Does not account for non-standard lapse rates or temperature inversions.
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Frequently Asked Questions
This calculator is for educational and planning purposes only. Always refer to your aircraft's POH/AFM, current NOTAMs, and official weather briefings. No calculator is a substitute for pilot-in-command judgment or CFI guidance. Read our full Safety Disclaimer.
Last reviewed: July 2026
Density Altitude in Depth
Density altitude is the altitude at which your aircraft actually performs, as opposed to the altitude printed on the airport diagram. It is the single most important environmental factor a pilot evaluates before a takeoff on a warm day or from a high-elevation field, because it silently governs how much runway you will need, how steeply you will climb, and how much power the engine can produce. The concept ties together three separate influences — altitude, temperature, and humidity — into one number that describes how dense the air is. It is a way of understanding the conditions; it is not, by itself, the input every performance chart asks for.
The reason density altitude deserves so much attention is that the flight instruments never warn you about it. The airspeed indicator, tachometer, and manifold pressure gauge can all read normally while the airplane quietly underperforms. Only a deliberate preflight calculation reveals the true picture, which is why the FAA Pilot's Handbook of Aeronautical Knowledge treats density altitude as a foundational performance concept every certificated pilot must understand.
Step-by-Step: How the Calculation Works
The calculation proceeds in two stages. First, field elevation is converted to pressure altitude by adjusting for the current altimeter setting: roughly 1,000 feet is added for every inch of mercury the setting sits below the standard 29.92 inHg, and subtracted for settings above it. This step removes the effect of the day's barometric pressure and expresses your height in the standard pressure reference the performance charts assume.
Second, pressure altitude is corrected for temperature. The standard (ISA) temperature at any pressure altitude is 15 degrees Celsius minus about 2 degrees for every 1,000 feet. Every degree the actual temperature exceeds that standard value adds roughly 120 feet of density altitude. When a dewpoint is supplied, this calculator additionally accounts for water vapor, which lowers air density slightly and therefore raises density altitude on humid days.
More Worked Examples
Example 1 — A cool morning at a low field
Field elevation 800 ft, altimeter 30.12 inHg, temperature 8°C. The altimeter is 0.20 inHg above standard, so pressure altitude is about 800 − 200 = 600 ft. Standard temperature there is roughly 14°C, so the actual 8°C is 6 degrees below standard, subtracting about 720 ft. Density altitude is about −100 ft (this calculator returns −97 ft) — roughly 900 ft below the field elevation, so the air is denser than standard for this field. Cooler, denser air can improve performance, but actual takeoff and climb performance must still be evaluated with the applicable aircraft charts, loading, configuration, technique, aircraft condition, runway, and wind assumptions.
Example 2 — A hot afternoon in the mountains
Field elevation 6,000 ft, altimeter 29.92 inHg, temperature 34°C. Pressure altitude equals field elevation at 6,000 ft. Standard temperature there is about 3°C, so 34°C is 31 degrees above standard, adding roughly 3,720 ft. Density altitude is near 9,700 ft (this calculator returns 9,706 ft). A normally aspirated trainer can be expected to have substantially reduced climb performance. When you open the performance charts, use the inputs the chart specifies: many charts are entered with pressure altitude (here 6,000 ft) and outside-air temperature (34°C), and the chart itself accounts for the temperature effect — entering 9,700 ft on such a chart and then also applying the temperature would double-count it. Use density altitude only if the chart explicitly calls for it.
Pilot Decision-Making Context
Density altitude helps describe the effect of air density on performance, and a high figure is a strong prompt to look closely at the go/no-go decision. To find expected distances and climb, use the inputs and procedure specified by your particular aircraft’s current POH/AFM performance chart. Many charts require pressure altitude and outside-air temperature; do not substitute density altitude unless the chart explicitly calls for it. The educational result here does not establish takeoff distance, climb capability, or operational suitability. Once you have the chart values, add margin for technique and aircraft condition, and compare the result to the runway available and the terrain off the departure end. If the required ground roll or the obstacle-clearance distance approaches what the runway offers, the safe answer is to change the plan: depart in the cooler early morning, reduce weight by carrying less fuel or fewer passengers, or choose a longer runway.
The same number also shapes in-flight expectations. A high density altitude means a higher true airspeed for a given indicated airspeed, a reduced service ceiling, and a shallower climb gradient over rising terrain. Building the habit of computing density altitude first gives you realistic expectations before you ever advance the throttle.
When to Use a More Advanced Method
This calculator uses the standard lapse rate and a proven approximation suitable for preflight planning. For certification-grade performance work, or for turbocharged and turbine aircraft whose engines behave differently with altitude, always defer to the specific performance charts and procedures in your aircraft flight manual. Background: FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C, 2023), Chapter 11, Aircraft Performance, which covers density altitude and the use of manufacturer performance charts.
More Questions Answered
Does density altitude affect landing as well as takeoff?
Yes. Higher density altitude increases your true airspeed and therefore your groundspeed on final for a given indicated approach speed, which lengthens the landing roll. It also reduces the effectiveness of a go-around climb, so the same caution applies to arrivals at high, hot fields.
Why does humidity raise density altitude?
Water vapor molecules are lighter than the nitrogen and oxygen molecules they displace, so moist air is slightly less dense than dry air at the same temperature and pressure. Entering a dewpoint lets the calculator include this effect, which is typically a few hundred feet on a hot, humid day.
Is density altitude the same as pressure altitude?
No. Pressure altitude accounts only for barometric pressure. Density altitude is pressure altitude further corrected for temperature (and optionally humidity). On a standard-temperature day the two are equal; on a hot day density altitude is higher.
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