Pressure altitude

Pressure altitude from field elevation and the altimeter setting, exact from the standard atmosphere, with the 1,000 ft per inch rule 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

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.

5,112ft

Pressure altitude is 5,112 ft. The 1,000 ft per inch rule gives 5,120 ft, off by 8 ft.

Station pressure
Rule of thumb
Rule-of-thumb error

Provenance

Computed by: aviation.altimetry.pressure-altitude 1.1.0, core 0.1.0
Model: ISA pressure-height relation (ISA-derived constants 145,442.16 ft and 0.190263), layered above 36,089 ft
Accuracy: Exact to the ISA definition. The NWS constant set (145,366.45 ft, 0.190284) differs by up to about 12 ft. Planning aid, not certified for navigation.
Notes: None
Cites: International Civil Aviation Organization, Manual of the ICAO Standard Atmosphere (extended to 80 kilometres (262 500 feet)); Federal Aviation Administration, Aviation Weather Handbook, FAA-H-8083-28B; 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: ISA pressure-height relation (ISA-derived constants 145,442.16 ft and 0.190263), layered above 36,089 ft

Show your work

Station pressure
p = 1013.25 × ((QNH/1013.25)^0.190284 − elevation × 6.8756e-6)^(1/0.190284)
p from QNH 29.80 inHg at 5,000 ft = 839.53 hPa
Pressure altitude
PA = the ISA altitude whose pressure is p
PA for p = 839.53 hPa = 5,112 ft

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

Accuracy: Exact to the ISA definition. The NWS constant set (145,366.45 ft, 0.190284) differs by up to about 12 ft. Planning aid, not certified for navigation.

When to use this: Use this when a performance chart, a flight level, or another calculation asks for pressure altitude rather than field elevation: it is the altitude the airplane would read with the altimeter set to 29.92 inHg, which is what the standard atmosphere is indexed by. It is also the first step into density altitude, true airspeed, and the airspeed and altimetry tools here.

Limitations: It converts an altimeter setting to a height in the standard atmosphere and nothing more: it does not know the temperature, so it is not the true altitude, and it does not apply the cold-temperature correction an approach needs. Two constant sets are in use and they differ by about 12 ft; this reports the ISA-derived set unless you ask for the NWS one.

Worked example: A 5,000 ft field with the altimeter at 29.80 inHg. Source: add-aviation-suite altimetry scenario: 5,112 ft (±1 ft); rule of thumb 5,120 ft. It is golden test vector v023, and every build checks the tool still gives its answer within its tolerance.

You enter

Altimeter setting: 29.80 inHg
Field elevation: 5000 ft

You get

Pressure altitude: 5,112 ft
Station pressure: 24.79 inHg
Rule of thumb: 5,120 ft
Rule-of-thumb error: 8 ft

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: 25 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)
Earth radius for geopotential altitude: 6356766 m — Manual of the ICAO Standard Atmosphere (Doc 7488)

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.
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.
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).

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

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