On hot, high and humid days aircraft perform as if the airfield were much higher: take-off runs lengthen and climb rates fall. Density altitude is that “as-if” altitude, and pilots check it before every hot-day departure.
How to use the Density Altitude Calculator
- Field elevation
- Altimeter setting (QNH)
- Outside air temperature
- Dew point
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Enter the field elevation, the altimeter setting (QNH), the outside air temperature and the dew point.
Inputs explained
| Field | What to enter |
|---|---|
| Field elevation | Units: ft, m |
| Altimeter setting (QNH) | Units: inHg, hPa |
| Outside air temperature | Units: °C, °F, K |
| Dew point | Units: °C, °F, K |
What each result means
- Station pressure = (([Altimeter setting (QNH)]÷100)^0.190263 – 8.417286e-5×[Field elevation])^(1÷0.190263)
- Vapour pressure = 6.112×exp(17.62×([Dew point])÷(243.12 + ([Dew point])))
- Air density = ([Station pressure] – [Vapour pressure])×100÷(287.058×([Outside air temperature] + 273.15)) + [Vapour pressure]×100÷(461.495×([Outside air temperature] + 273.15))
- Pressure altitude = (1 – ([Station pressure]÷1013.25)^0.190284)×145366.45×0.3048
- Density altitude = (44.3308 – 42.2665×[Air density]^0.234969)×1000
Example values
How the main result changes when Field elevation changes and everything else stays at the example values above:
| Field elevation (ft) | Density altitude (ft) |
|---|---|
| 750 | 2,634.0706 |
| 1,125 | 3,093.4296 |
| 1,500 | 3,552.5403 |
| 1,875 | 4,011.4026 |
| 2,250 | 4,470.0163 |
| 3,000 | 5,386.4981 |
Formula
p_stn = (QNH^{0.190263} − 8.417286×10⁻⁵·elev)^{1/0.190263}, ρ = p_d/(R_dT) + p_v/(R_vT)
DA (km) = 44.3308 − 42.2665·ρ^{0.234969}
Worked example
Inputs — Field elevation: 1,500 ft; Altimeter setting (QNH): 30.12 inHg; Outside air temperature: 30 °C; Dew point: 15 °C.
Results — Station pressure = 965.9578 hPa; Vapour pressure = 17.01672 hPa; Air density = 1.10263 kg/m³; Pressure altitude = 1,316.145 ft; Density altitude = 3,552.5403 ft.
Key terms
- Density altitude
- Altitude in the standard atmosphere with the same air density.
Frequently asked questions
Why does density altitude matter?
Aircraft and engines perform according to air density, not the field's elevation.
What makes density altitude high?
High elevation, high temperature, low pressure and humidity.
What is pressure altitude?
Altitude in the standard atmosphere with the same pressure.
How much does it change per °C?
Roughly 120 ft per °C above standard temperature.