Density Altitude Calculator
Find the density altitude from pressure altitude and temperature — the altitude your aircraft, wings and engine actually feel.
How it works
ISA temp = 15 − 1.98 × (PA ÷ 1000) · Density altitude = PA + 120 × (OAT − ISA temp)
Density altitude is pressure altitude corrected for temperature — the altitude at which the air density matches what the aircraft is experiencing. Hot air is less dense, so a warm day at a modest field elevation can make the aeroplane perform as if it were thousands of feet higher. High density altitude lengthens takeoff and landing distances, flattens the climb rate and reduces engine power, which is why it is a leading factor in mountain and summer accidents.
Worked example
At 5,000 ft pressure altitude the ISA temperature is 15 − 1.98 × 5 ≈ 5 °C. On a 25 °C day the deviation is +20 °C, so density altitude = 5,000 + 120 × 20 = 7,400 ft. The wings and engine behave as though the runway were at 7,400 ft.
Sources: Density altitude — Wikipedia
Frequently asked questions
Why does density altitude matter for takeoff?
Lift, thrust and propeller efficiency all depend on air density. High density altitude means less dense air, so the aircraft needs more runway to accelerate to a higher true liftoff speed and then climbs more weakly. Performance charts are read at density altitude, not field elevation.
What is a "high" density altitude?
There is no single threshold, but any density altitude several thousand feet above field elevation deserves attention. On hot days at high-elevation airports, density altitude can exceed 10,000 ft even when the ground is far lower.
Does humidity affect it?
Yes, though less than temperature and pressure. Moist air is slightly less dense than dry air, which nudges density altitude up. This 120-ft-per-degree method ignores humidity, so treat the result as a close estimate.
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This calculator is for educational purposes. Double-check important results before acting on them.