Density Altitude Calculator
Calculate density altitude and air density from pressure altitude, temperature, and humidity — the essential aviation performance tool.
Enter pressure altitude, outside air temperature, and relative humidity to calculate the density altitude that determines aircraft performance.
Density Altitude Calculator
Calculate density altitude and air density from pressure altitude, temperature, and humidity — the essential aviation performance tool.
About the Density Altitude Calculator
Density altitude is the altitude in the International Standard Atmosphere (ISA) at which a given air density would be found. It is not a physical altitude — your aircraft sits on the runway at 5,000 ft elevation whether the air is cold or hot — but it determines how your aircraft performs because engine power output, propeller efficiency, and aerodynamic lift all depend on air density. A high density altitude means thin, low-density air; a low density altitude means dense, high-performance air.
The concept is critical in aviation because aircraft performance charts are based on ISA standard conditions. When you calculate density altitude, you convert your actual atmospheric conditions into a single number that you can use directly with performance charts, reducing complex meteorology to a practical planning tool. Pilots must account for density altitude when computing takeoff distance, climb rate, service ceiling, and landing performance — underestimating it in hot, humid, high-altitude conditions has contributed to numerous accidents.
Three factors drive density altitude. Pressure altitude is the altitude indicated by your altimeter when set to the standard setting of 29.92 inHg (1013.25 hPa). As you ascend, pressure falls and so does air density. Temperature is equally important: hot air is less dense than cold air at the same pressure. A day that is 30°C above ISA standard can raise density altitude by 3,500 ft or more. Humidity has a smaller but real effect. Water vapour (molecular weight 18) is lighter than dry air (effective molecular weight ≈ 29), so humid air is slightly less dense than dry air at the same temperature and pressure — this is sometimes called the humidity correction to density altitude.
This calculator uses the ISA pressure model to find the actual atmospheric pressure at the entered pressure altitude, then applies the virtual temperature method to account for humidity. The air density is: ρ = (P − 0.3783·e) / (287.05·T), where P is pressure in Pascals, e is partial pressure of water vapour, and T is temperature in Kelvin. Density altitude is then derived from the ISA relationship between density and altitude.
As a rule of thumb, density altitude increases by about 120 ft for every 1°C above ISA standard temperature at a given pressure altitude, and the ISA standard temperature decreases at a lapse rate of roughly 2°C per 1,000 ft. At sea level the ISA standard is 15°C; at 5,000 ft it is 5°C; at 10,000 ft it is −5°C. On a hot summer day with high humidity at a high-elevation airport, density altitude can easily exceed physical altitude by 3,000–5,000 ft, dramatically extending takeoff roll and reducing climb performance.
Density Altitude Examples
How temperature and humidity affect density altitude at various pressure altitudes.
| Conditions | Density Altitude | Notes |
|---|---|---|
| PA = 0 ft, OAT = 15°C, RH = 0% | ≈ 0 ft | ISA standard sea-level conditions. Air density = 1.225 kg/m³. Performance charts apply directly with no correction needed. |
| PA = 8000 ft, OAT = 30°C, RH = 40% | ≈ 11 700 ft | Hot, moderately humid conditions at a high-elevation airport. OAT is ~31°C above ISA standard at this altitude, adding roughly 3,700 ft to the density altitude. |
| PA = 2000 ft, OAT = 35°C, RH = 80% | ≈ 5 300 ft | Hot and very humid conditions. Both elevated temperature and humidity reduce air density, making performance significantly worse than the 2,000 ft elevation suggests. |
| PA = 3000 ft, OAT = −10°C, RH = 20% | ≈ 650 ft | Cold, dry winter conditions. OAT is well below ISA standard, resulting in dense air and a density altitude much lower than the physical elevation — excellent performance. |
How to Use the Density Altitude Calculator
- Set your altimeter to 29.92 inHg (1013.25 hPa) and read the indicated altitude — that is your pressure altitude. Enter it in feet.
- Enter the outside air temperature (OAT) in degrees Celsius. Use the temperature at your current location, not the sea-level temperature.
- Enter the relative humidity as a percentage (0–100). If humidity data is unavailable, 0% gives a conservative estimate without the humidity correction.
- Click Calculate. The result shows density altitude in feet, air density in kg/m³, the ISA standard temperature at your pressure altitude, and the deviation from ISA.
- Compare density altitude to your aircraft's performance charts and POH data to determine takeoff distance, climb rate, and other performance figures.
Density Altitude FAQ
Why does density altitude matter for pilots?
Aircraft performance — engine power, propeller thrust, and wing lift — all depend on air density. Performance charts are based on ISA standard density. Density altitude translates your actual conditions into the equivalent ISA altitude, so you can read performance data directly from charts. High density altitude means reduced performance, longer takeoff rolls, and slower climbs.
How does temperature affect density altitude?
Hot air expands and becomes less dense. For every 1°C above the ISA standard temperature at a given pressure altitude, density altitude increases by approximately 120 ft. On a day 20°C above standard, density altitude is about 2,400 ft higher than pressure altitude — a critical factor at high-elevation airports in summer.
Does humidity significantly affect density altitude?
Humidity has a smaller effect than temperature but is not negligible. Humid air contains lighter water vapour molecules (molecular weight 18) replacing heavier nitrogen and oxygen molecules (average ≈29), making the air mixture less dense. At high temperatures with high humidity, the humidity correction can add 200–500 ft to density altitude compared to dry conditions.
What is ISA deviation and why is it shown?
ISA deviation (or ISA+/−) is the difference between your actual OAT and the ISA standard temperature at the same pressure altitude. ISA standard temperature decreases at 2°C per 1,000 ft from 15°C at sea level. A positive ISA deviation (e.g., ISA+15) means hotter-than-standard air and therefore higher density altitude and reduced performance.
What is considered a high density altitude airport?
Airports above 5,000 ft MSL are often called 'high-altitude' airports, but density altitude can exceed 5,000 ft even at sea-level airports on hot, humid days. Any density altitude above 5,000 ft warrants careful performance planning. Famous examples include Lukla in Nepal (9,383 ft elevation) and Telluride Regional Airport in Colorado (9,070 ft elevation).
How is density altitude calculated without a computer?
A simple approximation is: DA = PA + 120 × (OAT − ISA_temp), where ISA_temp = 15 − 0.00198 × PA. This rule-of-thumb ignores humidity but is accurate within a few hundred feet. Pilots also use the E6B flight computer or manufacturer-supplied density altitude charts. This online calculator applies the full physical formula including the humidity correction.