Density altitude

How high the airplane feels: density altitude from field elevation, altimeter setting, and temperature, with optional dew point, and the rules of thumb beside it.

Planning and education aid. Not for primary navigation. Full disclaimer

A published result changed on 2026-09-23: Station pressure now comes from the altimeter-setting relation instead of a sea-level ratio shortcut. The worked example moved from 5,108 to 5,112 ft pressure altitude and 7,932 to 7,937 ft density altitude; at an 8,000 ft field with 28.20 inHg the old answer was 90 ft low. Changelog

Assumes dry air unless you give a dew point. Add the dew point and the tool uses virtual temperature. On a humid day the dry-air answer reads a few hundred feet low, which matters most at a high field on a hot afternoon. ICAO Doc 7488, the standard atmosphere the altimetry is defined against.

Computing your own values needs JavaScript and WebAssembly. The worked example below was computed when this page was built, and the documentation under "How we got this" applies.

7,937ft

Density altitude is 7,937 ft, about 2,900 ft higher than the field. Expect a longer takeoff roll and weaker climb. Assumes dry air.

The 120 ft per °C rule of thumb gives 8,128 ft (191 ft high).

Assumes dry air. Add a dew point to include humidity, which raises density altitude.

Above the field
Pressure altitude
ISA temperature
ISA deviation
118.8 ft per °C rule
118.8 rule error

Provenance

Computed by: aviation.altimetry.density-altitude 1.1.0, core 0.1.0
Model: Air density from station pressure and (virtual) temperature, inverted through the layered ISA density profile; Magnus vapor pressure (Alduchov and Eskridge 1996)
Accuracy: Exact to the ISA definition for dry air; with humidity, vapor pressure is within 0.4% from -40 to 50 °C. Planning aid, not certified for navigation.
Notes: 1 shown with the answer
Cites: International Civil Aviation Organization, Manual of the ICAO Standard Atmosphere (extended to 80 kilometres (262 500 feet)); Federal Aviation Administration, Pilot's Handbook of Aeronautical Knowledge, FAA-H-8083-25C; Federal Aviation Administration, Aviation Weather Handbook, FAA-H-8083-28B; Alduchov, O. A., and Eskridge, R. E., Journal of Applied Meteorology, Improved Magnus form approximation of saturation vapor pressure

Something look off?

How we got thisFormula, worked example, sources, and proof

Model: Air density from station pressure and (virtual) temperature, inverted through the layered ISA density profile; Magnus vapor pressure (Alduchov and Eskridge 1996)

Show your work

Station pressure
p = ((QNH/1013.25)^0.190284 − elevation × 6.8756e-6)^(1/0.190284) × 1013.25
p from QNH 1,009.14 hPa and elevation 1,524 m = 839.53 hPa
Pressure altitude
PA = the ISA altitude whose pressure is p
PA for p = 839.53 hPa = 5,112 ft
Air density
$ρ = p / (R × Tv)$
ρ = 83,953.5 / (287.05287 × 303.15) = 0.9648 kg/m³
Density altitude
DA = the ISA altitude whose density is ρ
DA for ρ = 0.9648 kg/m³ = 7,937 ft

The same steps an agent gets from the MCP server with explain: true.

Accuracy: Exact to the ISA definition for dry air; with humidity, vapor pressure is within 0.4% from -40 to 50 °C. Planning aid, not certified for navigation.

When to use this: Reach for this before a takeoff or climb on a warm day, at a high field, or when the air is humid: density altitude is the altitude the airplane's wing and engine behave as though they are at, and the POH performance charts are read at that altitude rather than at the field elevation. Run it with the field elevation, the altimeter setting, and the temperature you actually have, and again with the dew point when the air is muggy.

Limitations: This is the air, not the airplane: it does not know your weight, your runway, or your propeller, and it does not produce a takeoff or climb number. Take the density altitude it gives to the performance charts in your POH or AFM, which govern. The humidity correction uses vapor pressure and is small next to the temperature effect, and nothing here accounts for wind, slope, or surface.

Worked example: A 5,000 ft field at 30 °C with the altimeter at 29.80 inHg. Source: add-aviation-suite altimetry scenario: PA 5,112 ft, ISA 4.87 °C, DA 7,937 ft (±5 ft), 118.8 rule 8,098 ft. It is golden test vector v022, and every build checks the tool still gives its answer within its tolerance.

You enter

Altimeter setting: 29.80 inHg
Field elevation: 5000 ft
Outside air temperature: 30 °C

You get

Density altitude: 7,937 ft
Above the field: 2,900 ft
Pressure altitude: 5,112 ft
ISA temperature: 4.9 °C
ISA deviation: 25.1 °C
118.8 ft per °C rule: 8,098 ft
118.8 rule error: 161 ft
120 ft per °C rule: 8,128 ft
120 rule error: 191 ft
Air density: 0.96476 kg/m³

Review: Not yet independently reviewed by a flight instructor (CFI).

Last verified: 2026-09-18, when a maintainer last confirmed this tool's sources at the issuer. See the sources ledger.

Status: version 1.1.0, core 0.1.0. See this tool in the verification report.

Changes

2026-09-23, result change: Station pressure now comes from the altimeter-setting relation instead of a sea-level ratio shortcut. The worked example moved from 5,108 to 5,112 ft pressure altitude and 7,932 to 7,937 ft density altitude; at an 8,000 ft field with 28.20 inHg the old answer was 90 ft low. Changelog
2026-09-19, changed: Pressure altitude, density altitude, runway crosswind and headwind, and the wind triangle are now stable. Each matches the worked examples in the FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C) and at least 20 vectors from a separate implementation. Results are unchanged. Changelog

Checked against: 21 golden test vectors (download the test vectors, each with its source and tolerance). See how results are checked and every source.

Constants this tool assumes

Values you do not enter, and where each comes from.

Sea-level pressure P0: 101325 Pa — Manual of the ICAO Standard Atmosphere (Doc 7488)
Sea-level temperature T0: 288.15 K — Manual of the ICAO Standard Atmosphere (Doc 7488)
Standard gravity g0: 9.80665 m/s2 — Manual of the ICAO Standard Atmosphere (Doc 7488)
Gas constant for dry air R: 287.05287 J/(kg K) — Manual of the ICAO Standard Atmosphere (Doc 7488)
Tropospheric lapse rate: -0.0065 K/m — Manual of the ICAO Standard Atmosphere (Doc 7488)
Magnus coefficient a (saturation vapor pressure): 17.625 — Alduchov and Eskridge (1996) Magnus form
Magnus coefficient b: 243.04 degC — Alduchov and Eskridge (1996) Magnus form
Magnus coefficient c: 6.1094 hPa — Alduchov and Eskridge (1996) Magnus form

Sources

Manual of the ICAO Standard Atmosphere (extended to 80 kilometres (262 500 feet)), International Civil Aviation Organization, 3rd edition, Doc 7488/3. Section 2 (defining constants and equations) and Table 1. Paid only.
Pilot's Handbook of Aeronautical Knowledge, FAA-H-8083-25C, Federal Aviation Administration, FAA-H-8083-25C. Aircraft Performance and Navigation chapters (pressure and density altitude, wind triangle).
Aviation Weather Handbook, FAA-H-8083-28B, Federal Aviation Administration, FAA-H-8083-28B. Section 8.4 (altimetry), section 3.4.2.14 and tables 3-17 and 3-18 (flight categories), section 24.4 (METAR and SPECI), section 27.2 (FB winds and temperatures aloft), and section 27.4 (TAF). Read free.
Improved Magnus form approximation of saturation vapor pressure, Alduchov, O. A., and Eskridge, R. E., Journal of Applied Meteorology, Vol. 35, No. 4. pp. 601-609, equation 21 (AERK coefficients).

Terms

ISA: International Standard Atmosphere: A reference atmosphere: 15 °C and 1013.25 hPa at sea level, cooling 6.5 °C per kilometer up to 11 km. Altimeters and performance charts are built on it. Source: Manual of the ICAO Standard Atmosphere (Doc 7488)

Learn the concept: How to read a METAR, What is density altitude?, What is pressure altitude?

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