QNH, QFE, and QNE

Model: QFE = p_ISA(elevation + PA(QNH)): an altimeter set to QNH reads the field elevation on the ground, which is the relation that defines QNH, and QNH from QFE the other way; QNE is the ISA altitude of QFE. From QFE the NWS formula is also shown: (P − 0.3) × (1 + (1013.25^0.190284 × 0.0065 ÷ 288) × h ÷ (P − 0.3)^0.190284)^(1/0.190284), P in hPa and h in m

Show your work

1. Pressure altitude of QNH

   PA(QNH) = the ISA altitude whose pressure is QNH

   PA(1,013 hPa) = 2.1 m

2. QFE

   QFE = p_ISA(elevation + PA(QNH))

   p_ISA(304.8 m + 2.1 m) = 976.9 hPa

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

Accuracy: Exact for the ISA relation. The NWS formula is the same relation with its own constants, less 0.3 hPa for the barometer's height, so it reads about 0.3 hPa (0.01 inHg) lower

Worked example: QNH 1013 hPa at a 1,000 ft airport. Source: add-aviation-suite QFE scenario: QFE by the ISA pressure-height relation; with QFE set the altimeter reads 0 ft on the ground. It is golden test vector v010, and every build checks the tool still gives its answer within its tolerance.

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 1.1.1, core 0.1.0. See this tool in the verification report.

Changes

• 2026-09-23, fixed: An altimeter setting of A2980 showed as 29.8 inHg. Settings are given to hundredths (FAA-H-8083-28B section 24.4.3.11), so the METAR decoder and the QNH of the Q-codes tool now keep the trailing zero: 29.80 inHg. In hPa they read as before. The METAR decoder is now version 1.1.1 and the Q-codes tool 1.1.1. Changelog
• 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

Checked against: 10 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.
• Altimeter Setting (WxCalc), National Weather Service, El Paso, Web calculator documentation. The altimeter setting formula from station pressure (hPa) and elevation (m).

Terms

NWS: National Weather Service

The US government weather service, which runs the airport weather stations and computes their altimeter settings. Source: Aeronautical Information Manual

QFE: field pressure (Q code)

The air pressure at the airport. With it set, an altimeter reads zero on the ground and height above the airport in the air. Source: Aeronautical Information Manual

QNE: standard setting (Q code)

What an altimeter reads with 29.92 inHg (1013.25 hPa) set: the pressure altitude. On the ground it is the field's pressure altitude. Source: Aeronautical Information Manual

QNH: altimeter setting (Q code)

The pressure setting that makes an altimeter read the airport's elevation on the ground, and altitude above sea level in the air. Source: Aeronautical Information Manual

Experimental means this tool has not yet met the stable bar: at least 20 golden vectors, differential tests, and an independent worked example.