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Density altitude calculator with dew point

This density altitude calculator follows the National Weather Service formulas: station pressure from the altimeter setting, virtual temperature from the dew point, then the density altitude. At a 5,000 ft field with 29.92 inHg, 30 °C and a dew point of 10 °C the air is as thin as at 7,997 ft in the standard atmosphere.

Example: Elevation unit: feet · Field elevation 5,000 · Altimeter setting (QNH) 29.92 · Temperature unit: °C · Outside air temperature 30 · Dew point 10 → Density altitude: Density altitude 7,997 ft (2,437 m). Source: NOAA National Weather Service (El Paso) – Density Altitude: vapor pressure, virtual temperature and density altitude formulas (read 09.10.2026). Updated: .

inHg (e.g. 29.92) or hPa (e.g. 1013) – values above 100 count as hPa
from the METAR; equal to the temperature at 100 % humidity
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Result

Density altitude
Density altitude 7,997 ft (2,437 m)
Details
ItemValue
Density altitude7,997 ft = 2,437 m
Pressure altitude5,002 ft = 1,525 m
Density altitude minus field elevation2,997 ft higher
Station pressure842.9 hPa = 24.89 inHg
Altimeter setting1,013.2 hPa = 29.92 inHg
Vapor pressure at the dew point12.28 hPa
Virtual temperature31.7 °C
Calculated estimate with the NWS formulas. A high density altitude means a longer take-off run and a lower climb rate (FAA); take-off and climb performance always come from the aircraft’s POH/AFM charts – in high humidity the FAA advises adding 10 % to the computed take-off distance.

How it is calculated

Density altitude is the altitude in the standard atmosphere at which the air has the same density as at your field. Heat, low pressure and humidity make the air thinner, so engines, propellers and wings perform as if the airplane were higher up. The calculator uses the formulas of the National Weather Service (El Paso office):

Examples (altimeter 29.92 inHg)

Field elevationTemperature / dew pointDensity altitude
0 ft15 °C / 0 °C96 ft
0 ft35 °C / 20 °C2,587 ft
2,000 ft30 °C / 15 °C4,406 ft
5,000 ft15 °C / 0 °C6,258 ft
5,000 ft30 °C / 10 °C7,997 ft
8,000 ft25 °C / 0 °C11,013 ft

In the 5,000 ft example the station pressure is 24.89 inHg (842.9 hPa), the vapor pressure 12.28 hPa and the virtual temperature 31.7 °C; the pressure altitude is 5,002 ft. In °F the same day reads 95 °F with a 50 °F dew point at 35 °C / 10 °C: 8,524 ft.

Why humidity matters

Water vapor is lighter than dry air. At 5,000 ft and 30 °C a dew point of 25 °C instead of 10 °C raises the density altitude from 7,997 ft to 8,280 ft. Even at sea level in standard conditions the formulas give a few dozen feet rather than exactly zero, because they are fitted approximations.

Pressure altitude

Pressure altitude only looks at pressure: (1 − (p ÷ 1013.25)^0.190284) × 145366.45 ft with p in hPa. Air density on its own is in the air density calculator; the dew point from relative humidity in the dew point calculator.

Frequently asked questions

How do you calculate density altitude?

Find the station pressure from elevation and altimeter setting, the virtual temperature from temperature and dew point, then use 145366 × (1 − (17.326 × p ÷ Tv)^0.235). At 5,000 ft, 29.92 inHg, 30 °C and 10 °C dew point the result is 7,997 ft.

What is the density altitude at sea level on a hot day?

At 0 ft with 29.92 inHg, 35 °C and a 20 °C dew point it is 2,587 ft.

Does humidity really change density altitude?

Yes. At 5,000 ft and 30 °C, a dew point of 25 °C instead of 10 °C adds 283 ft (8,280 instead of 7,997 ft).

What is the difference between pressure altitude and density altitude?

Pressure altitude corrects only for pressure; density altitude also corrects for temperature and humidity. In the 5,000 ft example: 5,002 ft versus 7,997 ft.

Can I enter the altimeter setting in hPa?

Yes. Values above 100 are read as hPa and converted with 1 inHg = 33.8639 hPa.

Can I plan a take-off with this?

Use it as an estimate only. Take-off distance and climb rate come from the POH/AFM performance charts of your aircraft.

Sources and legal basis

As of: · Editorial policy

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