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Density Altitude Calculator for Pilots

Calculate density altitude from elevation, altimeter setting, and OAT. Shows pressure altitude, ISA deviation, performance level, and humidity note.

Airport elevation from charts/plates

QNH from ATIS/AWOS (standard = 29.92)

Density Altitude — Moderate

3,040 ft

Expect 20–30% longer takeoff roll. Climb rate reduced.

Pressure Altitude

1,000 ft

ISA Temp at PA

13°C

Temp deviation

+17°C

Takeoff roll estimate: ~30% longer than sea-level standard day performance (~10% per 1,000 ft DA). Verify with POH density altitude charts.
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How to Use This Calculator

  1. 1

    Enter field elevation

    Enter your airport's published field elevation in feet (from charts, airport directory, or ATIS). This is the MSL elevation of the runway, not the above-ground height.

  2. 2

    Enter altimeter setting

    Enter the current altimeter setting in inches of mercury (inHg) from ATIS or AWOS. Standard atmosphere is 29.92 inHg. Low pressure (below 29.92) increases pressure altitude and density altitude; high pressure decreases it.

  3. 3

    Enter outside air temperature

    Enter the current outside air temperature in °C or °F. Temperature has the largest single effect on density altitude after elevation — hot days dramatically increase DA. Use actual surface temperature, not forecast.

  4. 4

    Add dew point for humidity estimate

    Optionally enter the dew point from ATIS/METAR. When dew point is close to the OAT (small spread), humidity is high and actual density altitude will be somewhat higher than the dry-air calculation.

What Each Value Means

Pressure Altitude (feet MSL)
The altitude indicated when the altimeter is set to 29.92 inHg (standard sea-level pressure). Calculated as: field elevation + (29.92 - QNH) × 1,000 feet. Used as the basis for density altitude calculation and flight level reporting above the transition altitude.
ISA Temperature (°C)
International Standard Atmosphere temperature at a given pressure altitude. At sea level: 15°C. Decreases at 2°C per 1,000 ft of pressure altitude (6.5°C per 1,000 m). ISA at 5,000 ft = 15 - 10 = 5°C. Actual OAT above ISA means lower air density and higher density altitude.
Density Altitude (feet)
The pressure altitude corrected for non-standard temperature. The altitude in the standard atmosphere that has the same air density as the actual conditions. Aircraft performance tables are referenced to density altitude — this is what the aircraft 'thinks' its altitude is for performance purposes.

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Frequently Asked Questions

What is density altitude and why does it matter?
Density altitude is the altitude at which the air density equals the actual air density at your location. Hot, humid, or high-elevation conditions produce lower air density — the air is 'thinner' — which degrades aircraft performance: reduced lift, reduced engine power output, longer takeoff roll, and lower climb rate. An aircraft performing at sea level on a standard day at 1,000 ft elevation on a hot day may actually perform as if it were at 5,000–6,000 ft.
How do you calculate density altitude?
Density altitude = Pressure Altitude + 120 × (OAT - ISA temperature). Pressure altitude = field elevation + (29.92 - altimeter setting) × 1,000. ISA temperature at a given pressure altitude = 15°C - 2°C per 1,000 ft. Example: airport at 2,000 ft, altimeter 29.72, OAT 35°C → PA = 2,000 + (29.92-29.72)×1,000 = 2,200 ft → ISA = 15 - 4.4 = 10.6°C → DA = 2,200 + 120×(35-10.6) = 2,200 + 2,928 = 5,128 ft.
What is a dangerous density altitude for light aircraft?
Most light aircraft (Cessna 172, Piper Cherokee) have significant performance degradation above 5,000 ft density altitude. Above 8,000 ft DA, takeoff distance can increase by 60%+ over sea-level performance. Above 12,000 ft DA, some naturally-aspirated aircraft cannot maintain adequate climb rate and may not safely depart short or obstructed runways. Always verify with POH density altitude performance charts before departure.
How does temperature affect density altitude?
Every 1°C rise in temperature above ISA standard increases density altitude by approximately 120 feet. On an ISA standard day (15°C at sea level), density altitude equals pressure altitude. On a hot day (ISA +20°C, i.e., 35°C at sea level), density altitude is roughly 2,400 ft above pressure altitude. Summer afternoon temperatures at high-elevation airports routinely produce density altitudes 3,000–5,000 ft above field elevation.
Does humidity affect density altitude calculations?
Yes, but the FAA standard formula omits humidity for conservatism. Humid air is less dense than dry air (water vapor molecules are lighter than N2 and O2), which increases effective density altitude. In hot, humid conditions with a small temperature-dew point spread, effective density altitude can be 200–500 ft higher than the dry-air formula indicates. For critical performance decisions near aircraft limits, add 200–400 ft to the calculated DA in high-humidity conditions.