Density altitude calculator
The altitude your aircraft's performance actually behaves as if it were at — the number that matters on a hot day at a high field.
How it works
Density altitude is pressure altitude corrected for temperature. Three steps:
- Pressure altitude = field elevation + (29.92 − altimeter) × 1,000
- ISA temperature at that altitude = 15 °C − 1.98 °C per 1,000 ft
- Density altitude follows from the density ratio σ = δ / θ, inverted against the ISA density profile
The familiar rule of thumb — add about 120 ft per °C above ISA — is shown alongside so you can see how close it is. It is good to within a couple of hundred feet across normal conditions, which is why it survives.
Worked example
A field at 5,000 ft, altimeter 29.92, air temperature 30 °C. Pressure altitude is 5,000 ft. ISA there is about 5 °C, so you are 25 °C hot, and density altitude comes out near 8,000 ft. Your aircraft climbs, accelerates and stops like it is at 8,000 ft — on a runway that is only 5,000 ft up.
Why it bites
Takeoff roll and climb rate both degrade, and they degrade together, which is what makes hot-and-high accidents so consistent. Density altitude also rises with humidity — water vapour is lighter than dry air — and that effect is not in this calculation or in most POH charts. On a hot, humid day treat the number as optimistic.
Live: the highest density altitude on Earth right now
Computed from every reporting station worldwide. Each row shows the field elevation and temperature that produced it, so you can see the calculation above working on real conditions.
Live: where the air is lying to you most
Density altitude minus field elevation — how much worse off you are than the chart suggests. This list is usually dominated not by mountain fields but by very hot ones near sea level, which is the whole reason density altitude is taught as a separate idea from elevation.
Live: the highest airports reporting weather right now
Field elevation alone, for comparison. Note how differently this list is ordered from the two above.
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- Pressure altitude calculator
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- Crosswind component calculator
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- Cloud base calculator
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For planning and study, not for operational use. Aircraft performance comes from your POH, not from a generic formula.