ISA temperature and deviation
The standard temperature at a pressure altitude (15 °C falling 1.98 °C per 1,000 ft to -56.5 °C), and the deviation of an outside air temperature.
Planning and education aid. Not for primary navigation. Full disclaimer
Experimental: not yet fully verified. How results are checked
The standard temperature at 41,000 ft is -56.5 °C.
Provenance
- Computed by
- aviation.altimetry.isa-temperature 1.0.0, core 0.1.0
- Model
- ICAO Standard Atmosphere layer temperatures
- Accuracy
- Exact to the ISA definition
- 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
Something look off?
How we got thisFormula, worked example, sources, and proof
Model: ICAO Standard Atmosphere layer temperatures
Accuracy: Exact to the ISA definition
Worked example: ISA temperature at FL410. Source: add-aviation-suite altimetry scenario: -56.5 °C above 36,089 ft. It is golden test vector v005, and every build checks the tool still gives its answer within its tolerance.
You enter
- Pressure altitude
- 41000 ft
You get
- ISA temperature
- -56.5 °C
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 1.0.0, core 0.1.0. See this tool in the verification report.
Checked against: 6 golden test vectors (download the test vectors, each with its source and tolerance). See how results are checked and every source.
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).
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)
Experimental means this tool has not yet met the stable bar: at least 20 golden vectors, differential tests, and an independent worked example.
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)