Density Altitude Calculator (pressure altitude, temperature & dew point)

Understanding the density altitude calculator — concept and principle

Density altitude is the altitude in the standard atmosphere that has the same air density as the air around you. It is what the wings, propeller and engine actually "feel", so it controls take-off distance and climb rate. This calculator finds pressure altitude and density altitude from field elevation, altimeter setting, temperature and dew point.

Heat and humidity thin the air, so a 5,000 ft field behaves like 7,872 ft.

How it is calculated

Station pressure = QNH × (1 − 0.0065 h ÷ 288.15)^5.2559

Pressure altitude = ISA height of the station pressure

ρ = (p − e) ÷ (287.05 T) + e ÷ (461.5 T)

e = 6.1094 × exp(17.625 Td ÷ (Td + 243.04)) hPa (Magnus formula)

Density altitude = (288.15 ÷ 0.0065) × [1 − (ρ ÷ 1.225)^0.235] m

h field elevation in m, T air temperature in K, Td dew point in °C; QNH in inHg (× 33.8639) or hPa.

The principle

An aircraft's performance depends on air density: fewer air molecules mean less lift, less propeller thrust and less engine power. Density falls with lower pressure and with higher temperature, and humid air is slightly less dense than dry air because water vapour is lighter. The International Standard Atmosphere (ISA) defines a reference profile of pressure, temperature and density with height. Density altitude converts your actual density back into the ISA height where that density would occur, giving one number that captures the combined effect.

Worked example

Default inputs: elevation 5,000 ft, QNH 30.02 inHg, 30 °C, dew point 10 °C.

QNH = 30.02 × 33.8639 = 1,016.6 hPa; station pressure = 845.9 hPa.
Pressure altitude = 4,912 ft; ISA temperature there = 5.3 °C, so the air is 24.7 °C warmer than standard.
Vapour pressure at a 10 °C dew point ≈ 12.3 hPa; air density = 0.967 kg/m³.
That is 78.9% of the sea-level standard density.
Density altitude = 7,872 ft = 2,399 m.

Each point is the calculator re-run with only “Field elevation (ft)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Field elevation (ft)	Density altitude (ft)
1,250	3,297
2,500	4,825
3,750	6,350
5,000	7,872
6,250	9,391
7,500	10,907
10,000	13,931

How to read the result

Here the aircraft will perform as if it were nearly 3,000 ft higher than the field. High density altitude means longer take-off runs, slower climbs and higher true airspeeds for the same indicated airspeed. Pilots check this on hot days at high airports. Use your aircraft's performance charts with these conditions to find actual take-off and climb figures.

Common mistakes

Confusing pressure altitude with density altitude.
Ignoring humidity on hot, humid days.
Using the temperature from a different time or place than the take-off.
Using the altimeter setting in the wrong unit.

Keep in mind: This is an estimate for planning. Always use the aircraft's approved performance data and margins required by regulations and good practice.

Frequently asked questions

Why does hot weather hurt aircraft performance?

Hot air is less dense, so wings, propellers and engines have fewer air molecules to work with.

What is pressure altitude?

The altimeter reading with 29.92 inHg or 1013.25 hPa set, the ISA height of the current pressure.

Does humidity matter much?

It adds a few hundred feet on hot, humid days; temperature and pressure matter more.

Sources: ICAO Doc 7488/3, Manual of the ICAO Standard Atmosphere · FAA, "Density Altitude" (P-8740-02) · Alduchov & Eskridge (1996), Journal of Applied Meteorology 35: 601–609 (Magnus coefficients)

Checked 9 Nov 2026. ICAO Doc 7488/3, Manual of the ICAO Standard Atmosphere (T₀ 288.15 K, p₀ 1013.25 hPa, lapse 6.5 K/km, R 287.05287 J/(kg·K)); FAA P-8740-02, “Density Altitude” (definitions of pressure and density altitude, 29.92 inHg standard); vapour pressure: Alduchov & Eskridge (1996), J. Appl. Meteor. 35:601–609 (Magnus coefficients).

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