QNH, QFE and QNE: Altimeter Settings Explained

Updated: 2026-09-27 · First published: 2026-09-27 · About this site

The altimeter is a barometer with a scale in feet. It can only tell you your height above the pressure you have set on its subscale, which is why the same instrument can show altitude above sea level, height above the airfield, or a flight level — depending on a four-digit number a controller read to you. Get that number wrong and the instrument is still perfectly accurate; it is just measuring from the wrong place.

The three settings

QNH — altitude above mean sea level

QNH is the aerodrome pressure reduced to mean sea level using the standard atmosphere. Set it, and on the ground the altimeter shows the published aerodrome elevation. Airborne it shows altitude above sea level, which is what terrain, obstacles and minimum altitudes on the chart are measured from. QNH is the Q1013 group in a METAR: Q1013 means 1013 hPa. US stations report the equivalent as an altimeter setting in inches of mercury, A2992 = 29.92 inHg.

QFE — height above the aerodrome

QFE is the actual station pressure at the aerodrome reference point (or runway threshold). Set it and the altimeter reads zero on that runway. It is still used for circuits and approaches at some military and Eastern European aerodromes, and by some gliding and parachuting operations, because the numbers match the height above the field directly. It is not shown in a METAR; the tower gives it on request. Below sea level or at high-elevation airfields the QFE may be outside the subscale range, which is one reason airline operations standardised on QNH.

QNE — the standard setting for flight levels

QNE is 1013.25 hPa (29.92 inHg), the sea-level pressure of the ICAO standard atmosphere. With it set the altimeter reads pressure altitude. Above the transition altitude everyone flies on QNE so that two aircraft assigned FL350 and FL340 are separated by 1,000 ft of pressure regardless of the weather below them. Pressure altitude is also the input for performance calculations and, with temperature, for density altitude.

What a wrong setting costs

Near sea level, 1 hPa is about 27 ft and 1 inHg is about 1,000 ft. Suppose the QNH is 1003 but 1013 stayed on the subscale after descent. The altimeter reads about 270 ft higher than the aircraft actually is. On an approach with a 200 ft decision height that is the difference between the runway and the approach lights. The phrase drilled into instrument students — "high to low, look out below" — describes exactly this: flying from higher pressure into lower pressure without resetting.

The trend matters too. A METAR series with QNH falling 3 hPa per hour, which the pressure archive on each airport page will show you, is a warning that the setting you took an hour ago is already 80 ft stale. Ask for an update before the approach.

Converting hPa and inHg

1 inHg = 33.86 hPa. Quick mental conversion: 29.92 ≈ 1013, 30.00 ≈ 1016, 29.80 ≈ 1009. For anything precise use the table in your flight computer; a 0.03 inHg rounding error is 1 hPa, which is 27 ft. Note that A2992 in a METAR is an altimeter setting (QNH), while SLP132 in the remarks is sea-level pressure computed a different way and is not to be set on the altimeter.

Cold temperature: the error QNH cannot fix

The altimeter is calibrated for the standard atmosphere. In air colder than ISA the pressure surfaces are closer together, so a given pressure is reached at a lower true altitude than the instrument assumes. At −20 °C on a 3,000 ft indicated altitude above a sea-level field, the true altitude is about 360 ft lower. Operators publish cold-temperature correction tables and many approach charts now carry a minimum temperature below which the corrections are mandatory. Setting the correct QNH does nothing about this error; only the temperature correction does.

Transition altitude, layer and level

Climbing, you switch from QNH to 1013 at the transition altitude — a fixed published altitude, e.g. 3,000 ft in much of the UK, 5,000 ft in Germany, 18,000 ft in the USA and Canada. Descending, you switch from 1013 to QNH at the transition level, the lowest usable flight level above the transition altitude; it varies with the QNH of the day and is given by ATC or ATIS. The gap between them is the transition layer, at least 1,000 ft thick, in which no aircraft cruises. Confusing the two directions — setting QNH on the climb — is a common examiner question precisely because the consequence in the descent is real.

Reading the pressure on this site

Every airport page shows the current QNH from the METAR and, in the trends section, its recent history and the tendency. The pressure archive across many airports also lets you see a front moving through a region by the pressure minimum tracking east — compare LFPG Paris with EDDF Frankfurt on a frontal day. Regional differences of 10 hPa over a few hundred kilometres are normal on such a day, and each of those hectopascals is 27 ft.

Frequently asked questions

What is the difference between QNH and QFE?

QNH is the pressure at mean sea level derived from the aerodrome pressure; with QNH set the altimeter reads altitude above sea level and shows the aerodrome elevation on the ground. QFE is the actual pressure at the aerodrome reference point; with QFE set the altimeter reads zero on the runway and height above the aerodrome in the air.

What is QNE?

QNE is not a pressure but a setting: the standard atmosphere, 1013.25 hPa or 29.92 inHg. With QNE set the altimeter reads pressure altitude, expressed as a flight level. All aircraft above the transition level use it so that vertical separation is consistent regardless of the local weather.

How much altitude error does 1 hPa cause?

About 27–30 ft near sea level (the standard figure is 27 ft per hPa, or roughly 1,000 ft per inch of mercury). Setting 1003 when the QNH is 1013 makes the altimeter read about 270 ft too high — the aircraft is lower than indicated.

Why does the altimeter over-read in cold air?

Because cold air is denser and the pressure levels are packed closer together. Below about 0 °C the true altitude is lower than indicated, by roughly 4% per 10 °C below ISA. Cold-temperature corrections must be added to minimum altitudes on approach in cold weather.

What is the transition altitude?

The altitude at or below which the vertical position of an aircraft is expressed as an altitude on QNH. Above the transition level, position is expressed as a flight level on 1013.25. The layer between the two is the transition layer, and aircraft do not cruise in it.