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Density Altitude Calculator

Compute Pressure Altitude and Density Altitude from field elevation, QNH, and OAT. Understand ISA deviation and its impact on aircraft performance — critical for hot & high operations.

Density Altitude Calculator

Performance Warning: High density altitude significantly reduces engine power, propeller/rotor efficiency, and lift. Always check aircraft performance charts for the actual density altitude.
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ft
Pressure Altitude
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Density Altitude
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°C
ISA Temp at Elev
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°C
ISA Deviation

Understanding Density Altitude

Density Altitude is pressure altitude corrected for non-standard temperature. It represents the altitude at which the air density would be found in the International Standard Atmosphere (ISA). The higher the density altitude, the thinner the air — and the worse aircraft performance.

Pressure Altitude
PA = Elevation + (1013.25 − QNH) × 27

Approximate formula (QNH in hPa, result in feet). Each 1 hPa ≈ 27 ft.

Density Altitude
DA = PA + 118.8 × (OAT − ISA_Temp)

Each 1°C above ISA raises density altitude by ~120 ft.

ISA Temperature at Altitude
ISA_Temp = 15 − (Elevation_ft / 1000 × 1.98)

Standard lapse rate: −1.98°C per 1,000 ft (up to 36,089 ft).

Rule of Thumb: For every 1,000 ft of density altitude above sea level, expect roughly a 3% reduction in engine power (normally aspirated piston engines). Turbine engines are less affected but still impacted.

Performance Impact Reference

Density AltitudeApprox. Performance Impact
0 – 2,000 ftMinimal — standard operations
2,000 – 5,000 ftNoticeable — longer T/O roll
5,000 – 8,000 ftSignificant — check performance charts
8,000 – 12,000 ftSevere — may limit payload/fuel
> 12,000 ftCritical — possible inability to depart

Frequently Asked Questions

Aircraft performance depends on air density. Lower density means fewer air molecules per unit volume — engines produce less power (less oxygen for combustion), propellers generate less thrust, and wings produce less lift for a given speed. All performance charts are based on ISA conditions; density altitude tells you the "equivalent ISA altitude" for your actual conditions.

ISA deviation (ISA+/−) is the difference between the actual OAT and the ISA standard temperature at that altitude. A positive deviation (ISA+) means it is hotter than standard, increasing density altitude. A negative deviation (ISA−) means cooler air, which is beneficial for performance.

Yes. Water vapour is lighter than dry air, so high humidity reduces air density further, increasing density altitude. The effect is relatively small (typically 200–300 ft) but can be significant in hot, humid tropical conditions. Providing the dew point allows this calculator to estimate the correction.

"Hot and high" refers to operating from airports at high elevation in hot temperatures — both factors combine to produce very high density altitudes. Airports like Addis Ababa (7,625 ft) or Bogotá (8,361 ft) regularly challenge aircraft performance. Operators must use approved performance data and may need to restrict payload or wait for cooler temperatures.