Density Altitude Calculator
Density altitude is one of the most important numbers in aviation performance planning, particularly for piston-engine light aircraft. It describes the effective altitude that the aircraft "feels" in terms of air density, which directly controls engine power output, propeller efficiency, and aerodynamic lift. High temperature, low pressure, and high humidity all increase density altitude above field elevation. The FAA standard formula uses the pressure altitude and the deviation of actual temperature from the International Standard Atmosphere (ISA) temperature. Enter field elevation, altimeter setting (in inHg), and outside air temperature (in degrees Celsius) to compute pressure altitude, ISA temperature, and density altitude.
Density altitude formula
Pressure Altitude (ft) = Field Elevation + (29.92 - Altimeter Setting) x 1,000
ISA Temp (C) = 15 - (Pressure Altitude / 1,000) x 2
Density Altitude (ft) = Pressure Altitude + 120 x (OAT - ISA Temp)
The 120 ft per degree C factor comes from the FAA standard formula as published in the Pilot's Handbook of Aeronautical Knowledge. The ISA lapse rate used here is 2 degrees C per 1,000 ft (the simplified FAA version; the precise ISA value is 1.98 degrees C per 1,000 ft below the tropopause).
Density altitude performance effects
- For normally-aspirated piston engines, power output decreases approximately 3% per 1,000 ft of density altitude.
- Takeoff ground roll increases approximately 10% per 1,000 ft of density altitude above standard sea level.
- Rate of climb decreases significantly. Aircraft may be unable to maintain a positive climb rate at extreme density altitudes.
- Indicated airspeed for best climb (Vy) and best angle (Vx) remain constant, but true airspeed increases with density altitude.
Density altitude calculator: frequently asked questions
What is density altitude?
Density altitude is the pressure altitude corrected for non-standard temperature. It represents the altitude at which the density of the air would equal the actual air density. High density altitude means the air is thin, which reduces engine power, propeller efficiency, and lift, degrading aircraft performance.
How is density altitude calculated?
Density Altitude = Pressure Altitude + (120 x (OAT - ISA Temperature)). The FAA standard formula uses 120 ft per degree Celsius deviation from ISA. ISA temperature at a given altitude = 15 - (pressure altitude in 1,000 ft x 2).
How do I calculate pressure altitude?
Pressure Altitude = Field Elevation + (29.92 - Altimeter Setting) x 1,000. This converts your altimeter setting to the equivalent altitude on the standard altimeter setting of 29.92 inHg. You can also set your altimeter to 29.92 and read the pressure altitude directly.
Why does high density altitude affect aircraft performance?
Aircraft engines, propellers, and wings are all affected by air density. Piston engines produce less power in thin air. Propellers have less air to bite. Wings need more true airspeed to generate the same lift. All of this means longer takeoff rolls, slower climbs, and reduced payload capacity.
What is a dangerous density altitude?
At density altitudes above 5,000 ft, performance degradation becomes significant for light aircraft. At 7,000 to 10,000 ft density altitude, some piston aircraft may be unable to take off normally at maximum gross weight. Always check your aircraft's POH performance charts for the specific density altitude.
Official sources
- FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25B), Chapter 11 Weather Theory: faa.gov.
- FAA Safety Density Altitude Advisory: faasafety.gov.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.