Density altitude calculator

What the estimate shows

Density altitude is pressure altitude corrected for nonstandard temperature. It names the standard-atmosphere altitude where the air density matches the conditions you entered. Higher density altitude means thinner air, which means less lift from the wing, less power from a normally aspirated engine, and slower climb.

The number is most useful as a reference when reading the performance charts in a POH or AFM, because those charts are organized around pressure altitude and temperature or around density altitude directly.

How to use the calculator

Enter three values and the result updates as you type. The page URL mirrors the inputs, so a configured calculation can be bookmarked or shared.

Field elevation. Airport elevation in feet MSL, taken from the chart supplement or airport diagram. The range -2,000 to 25,000 ft covers fields below sea level as well as the highest US airports.

Altimeter setting. The reported setting in inches of mercury, 25 to 35 inHg. US METARs carry it in the A group, so A2992 means 29.92. Outside the US, the Q group reports hectopascals; divide by 33.8639 to convert to inHg.

Outside air temperature. Degrees Celsius. To convert Fahrenheit, subtract 32 and multiply by 5/9.

How the calculation works

The calculator runs three steps.

1. Pressure altitude: field elevation + (29.92 - altimeter setting) × 1,000. A setting above 29.92 lowers pressure altitude; a lower setting raises it.
2. Standard temperature: 15°C minus 2°C for each 1,000 ft of pressure altitude, the standard lapse rate.
3. Density altitude: pressure altitude + 120 × (actual temperature - standard temperature).

The 120 ft per °C factor is the standard planning approximation. The density altitude chart in the FAA Aviation Weather Handbook gives a more precise figure when chart precision is required.

Example calculation

A mountain field at 5,885 ft elevation on a warm day, altimeter setting 30.12 inHg, temperature 32°C.

1. Pressure altitude: 5,885 + (29.92 - 30.12) × 1,000 = 5,685 ft.
2. Standard temperature at 5,685 ft: 15 - (5.685 × 2) ≈ 3.6°C.
3. Density altitude: 5,685 + 120 × (32 - 3.63) ≈ 9,089 ft.

The air at that field on that afternoon is as thin as standard air near 9,100 ft. Performance planning should use figures for that altitude, not the elevation on the chart.

When pilots use it

Hot and high planning. Density altitude is the first check before reading takeoff, climb, and landing performance on a warm day at elevation, and it explains why a runway that works in winter can be short in summer.

Written exam preparation. FAA knowledge tests ask for density altitude read from a chart. Computing it directly and confirming with the chart is good practice.

A daily self-check. Comparing field elevation to density altitude shows at a glance how far conditions have drifted from standard.

Assumptions and limitations

The 120 ft per °C factor is a widely used planning approximation. Humidity is not modeled: humid air is less dense than dry air, so the true density altitude on a humid day is somewhat higher than the computed value. The standard 2°C per 1,000 ft lapse rate is assumed throughout.

The result describes air density only. It does not produce a takeoff distance, a climb gradient, or a go-around decision. Those come from the aircraft's own performance data under actual conditions.

Frequently asked questions

What is the difference between pressure altitude and density altitude?

Pressure altitude is the altitude shown on an altimeter set to 29.92 inHg. Density altitude corrects that figure for temperature. On a standard day the two are equal; on a hot day density altitude is higher.

Can density altitude be negative?

Yes. Cold temperatures and a high-pressure system at a low-elevation field can produce a negative density altitude, meaning the air is denser than standard sea-level air.

Does the calculator account for humidity?

No. Humid air is less dense, so high humidity raises the true density altitude above the computed value. Treat the result as a dry-air estimate.

Why enter the altimeter setting instead of pressure altitude?

Because the altimeter setting is what METAR and ATIS actually report. The calculator converts it to pressure altitude internally, which saves a step and a conversion error.

Sources and methodology

The formulas follow the standard-atmosphere relationships described in FAA references. The FAA Aviation Weather Handbook provides the density altitude chart used to verify the computation, and the Pilot's Handbook of Aeronautical Knowledge describes the relationship between density altitude and aircraft performance.

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