What is density altitude?

Density altitude is the altitude in the ICAO standard atmosphere at which the actual air density would occur. It directly governs aircraft performance: the higher the density altitude, the less lift, thrust, and engine power the aircraft produces. A density altitude of 8,000 ft at a sea-level airport on a very hot day is treated the same as being physically at 8,000 ft for performance purposes.

What is pressure altitude and how do I get it?

Pressure altitude is the altitude above the ICAO standard datum plane (29.92 in Hg / 1013.25 hPa). To read it, set your altimeter to 29.92 and read the indicated altitude. Alternatively, apply the approximate correction: subtract 27 ft per 0.01 in Hg below 29.92 (or add 27 ft per 0.01 in Hg above 29.92) to your field elevation.

Why does humidity affect density altitude?

Water vapor (H₂O, molecular weight 18) is lighter than dry air (average molecular weight ~29). High humidity displaces heavier nitrogen and oxygen molecules, reducing air density. The moisture correction is modest in temperate conditions but measurable in hot, humid climates — sometimes adding 300–500 ft to the density altitude reading.

What density altitude is considered dangerous?

There is no universal threshold, as it depends on the specific aircraft. As a rule of thumb, pilots should pay close attention above 5,000 ft density altitude for normally-aspirated piston aircraft. Many mountain airports recommend extra caution above 8,000 ft DA. Always consult your aircraft POH performance charts rather than relying on general rules.

How is ISA deviation calculated?

The ICAO standard atmosphere defines 15°C at sea level with a lapse rate of 2°C per 1,000 ft. Standard temperature at a given pressure altitude = 15 − (2 × altitude_in_thousands). ISA deviation is your actual OAT minus that standard temperature. A positive ISA deviation means it is hotter than standard, increasing density altitude.

Is this calculator accurate enough for flight planning?

Yes — it uses the standard ICAO density altitude formula identical to that published in FAA handbooks and used by aviation weather services. However, always cross-check against your aircraft POH and use current METAR/ATIS data for the actual OAT and altimeter setting.

Density Altitude Calculator

Name: Density Altitude Calculator
Availability: InStock
Author: Nham Vu

Enter pressure altitude, temperature, and dewpoint (or relative humidity) to compute density altitude for aviation performance planning.

Atmospheric Inputs

Pressure Altitude (ft)

Set altimeter to 29.92 in Hg and read indicated altitude.

Outside Air Temperature (OAT)

Standard at sea level is 15°C.

Moisture (optional)

Dewpoint in same unit as OAT. Leave blank to omit moisture correction.

ISA Standard Temperatures

Press. Alt.	Std Temp °C	Std Temp °F

Enter pressure altitude and temperature, then click Calculate.

Density altitude and performance category appear here.

Summary

Enter pressure altitude, temperature, and dewpoint (or relative humidity) to compute density altitude for aviation performance planning.

How it works

Enter pressure altitude in feet (field elevation corrected for altimeter setting, or read directly from your altimeter set to 29.92 in Hg).
Enter outside air temperature (OAT) in °C or °F — the tool converts automatically.
Optionally enter dewpoint in the same unit, or relative humidity (%), to add moisture correction.
The tool computes standard temperature at that pressure altitude, then calculates density altitude using the ICAO standard atmosphere formula.
Results include density altitude, temperature deviation from standard (ISA), and a performance risk category.
Compare your results against your aircraft POH performance tables to determine actual takeoff and climb distances.

Use cases

Determine aircraft takeoff performance on a hot summer day at a mountain airport.
Calculate density altitude before a high-altitude backcountry landing.
Assess helicopter performance margins in high, hot, and humid conditions.
Evaluate climb performance with a heavy load or non-standard engine configuration.
Cross-check density altitude shown on an aviation weather briefing.
Practice density altitude awareness during student pilot ground training.
Plan fuel and payload for operations at airports above 5,000 ft MSL.
Estimate performance degradation when OAT significantly exceeds ISA standard temperature.

Frequently Asked Questions

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Last updated: 2026-05-29 · Reviewed by Nham Vu