Density Altitude Calculator
The altitude your aircraft, engine or propeller 'feels' on a hot or low-pressure day, from field elevation, QNH and temperature.
Results
The dashed line marks the value you entered.
What this tool does
An aircraft's performance depends on air density, not on its altitude above the sea: on a hot day the air is thinner, so take-off runs get longer and climb rates fall as if the airfield were much higher. Density altitude is the height in the International Standard Atmosphere at which the air would have the density you have now. A 1000 ft airfield at 30 °C behaves like one at nearly 3000 ft. This uses dry air; humidity makes the air slightly less dense still, and the aircraft's own manual is what you must plan with.
Formula
ρ = p ÷ (R T) · DA = (T₀ ÷ L) × [1 − (ρ ÷ ρ₀)^0.234969] (ISA: T₀ = 288.15 K, L = 0.0065 K/m, ρ₀ = 1.225 kg/m³)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
el | Field elevation | ft |
qn | QNH (sea-level pressure) | hPa |
oat | Outside air temperature | °C |
DA | Density altitude | ft |
DM | Density altitude in metres | m |
PA | Pressure altitude | ft |
RH | Air density | kg/m³ |
RR | Density compared with sea-level standard | % |
IT | Standard (ISA) temperature at that altitude | °C |
Worked example
- Field elevation1000 ft
- QNH (sea-level pressure)1013.25 hPa
- Outside air temperature30 °C
- Density altitude2943 ft
- Density altitude in metres897 m
- Pressure altitude1000 ft
- Air density1.1229 kg/m³
- Density compared with sea-level standard91.7 %
- Standard (ISA) temperature at that altitude13.0 °C
Limitations
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.
- The default values are typical reference figures, not measurements of your situation. Replace them with your own data whenever you have it.