Density altitude calculator
Enter the field elevation, altimeter setting and temperature, get the density altitude.
Runway 17 has a heading of 170°. Use the same reference (true or magnetic) for the runway and the wind.
What is density altitude?
The FAA defines density altitude as pressure altitude corrected for nonstandard temperature: the altitude in the standard atmosphere where the air has the same density as the air you are in. An aircraft performs as if it were at that altitude. The FAA’s example is an airport at 500 feet with a density altitude of 5,000 feet: aircraft operating there perform as if the airport were at 5,000 feet.
How do you calculate density altitude?
Pressure altitude is the field elevation plus (29.92 − altimeter setting) × 1,000 feet. The standard temperature at that altitude is 15 °C minus about 2 °C per 1,000 feet (1.98 °C in the ICAO standard atmosphere, which this page uses). Density altitude is then the pressure altitude plus 120 feet for every degree Celsius the outside air temperature is above standard (AOPA). The FAA handbook’s own example, a field at 5,883 feet with 70 °F and an altimeter setting of 30.10, has a pressure altitude of 5,718 feet and a density altitude of about 7,700 feet.
Why does the calculator show two answers?
The rule of thumb is a straight-line shortcut. The ISA equations of the International Standard Atmosphere (temperature falling 6.5 °C per kilometer, pressure following the standard formula) give the altitude with exactly the same air density, and are the default here. They agree closely with the FAA’s rule-of-thumb chart: at 8,000 feet and 130 °F the chart says 13,800 feet and the equations 13,840 feet, while the 120-feet rule gives 14,640. The rule tends to overstate density altitude when it is hot and high.
Does humidity matter?
Humid air is less dense, but the FAA says humidity is not generally considered a major factor in density altitude computations and gives no chart for it. Its advice is to add 10 percent to your computed takeoff distance and expect a reduced climb rate if the humidity is high. This calculator uses dry air.
How much does high density altitude hurt performance?
Takeoff distance and landing roll get longer, climb rate drops and true airspeed rises for the same indicated airspeed. The FAA’s Koch chart gives one example for typical personal airplanes: at 100 °F and a pressure altitude of 6,000 feet, takeoff distance grows by 230 percent and climb rate falls by 76 percent. For real numbers, use the performance charts in your aircraft’s POH or AFM; this page does not estimate them.
How do I find the crosswind component?
Take the angle between the runway heading and the direction the wind is blowing from. The headwind is the wind speed times the cosine of that angle and the crosswind is the speed times the sine. The FAA handbook’s example is runway 17 (170°) with wind from 140° at 25 knots: a 30° angle, so about 22 knots of headwind and 12.5 knots of crosswind (13 on the chart). Compare the crosswind with the maximum demonstrated crosswind component in your AFM/POH.
For learning and awareness only — not for flight planning. Always use the performance charts in the aircraft’s Pilot’s Operating Handbook or Airplane Flight Manual. Sources: FAA, Pilot’s Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Chapter 11, Figures 11-2 and 11-3 and sample problems; FAA Safety Team, Density Altitude (FAA-P-8740-2); AOPA, Density Altitude; International Standard Atmosphere (ICAO), as tabulated in the FAA handbook. How we check our calculators.