Altimeter Settings: QNH vs QFE vs Standard Pressure

An altimeter can show a different reading without the aircraft climbing or descending. Change the pressure setting, and you change the reference behind the number.

That is why QNH, QFE and standard pressure matter. Each gives the reading a different meaning, and mixing them up can lead to incorrect calculations or reduced terrain clearance.

This guide explains how the settings work, when pilots change them, and how pressure and temperature affect the indication. We’ll also work through a climb-time question and the common traps that make altimetry harder than it needs to be.

Start With the Reference

Before reading an altimeter, ask: what is this number measured from? 

• Altitude is vertical distance above mean sea level (MSL).

• Height is vertical distance above a specified reference, such as the ground or a runway threshold.

• Elevation describes how high a point on the Earth’s surface sits above mean sea level.

For example, an aircraft at 3,500 ft AMSL, directly above terrain with an elevation of 1,000 ft, is 2,500 ft AGL. This assumes the altitude represents its actual position above sea level. 

For a closer look at these references, read MSL vs AGL: The Altitude Mistake Pilots Can’t Afford.

There is one more distinction to keep in mind. Indicated altitude is the altimeter reading; true altitude is the aircraft’s actual vertical distance above mean sea level. They can differ because a barometric altimeter converts air pressure into a reading using standard-atmosphere assumptions.

QNH, QFE and Standard Pressure Explained

The altimeter’s pressure setting determines the reference for its indication. Here is what each setting means in practice.

QNH

Altitude above mean sea level

QNH is the altimeter setting that makes the instrument indicate aerodrome elevation when the aircraft is on the ground. It is derived from aerodrome pressure using standard-atmosphere assumptions.

At an aerodrome with an elevation of 2,500 ft, an altimeter correctly set to local QNH should therefore read approximately 2,500 ft. In flight, QNH provides an altitude indication referenced to mean sea level. This lets pilots compare their indication with charted terrain elevations, obstacles and airspace limits.

QFE

Height above a specified aerodrome datum

QFE is the atmospheric pressure at the specified aerodrome or runway threshold elevation. Set it on the altimeter, and the instrument should read approximately zero at that datum.

In flight, the reading indicates height above that reference. Where local procedures use QFE, this can help pilots fly circuit heights or follow procedures expressed relative to the aerodrome or threshold. It does not continuously measure clearance above changing terrain beneath the aircraft.

Standard Pressure

A common reference for flight levels

Standard pressure (SPS) is 1013.25 hPa, often rounded to 1013 hPa in exam calculations. You may also see standard pressure labelled STD on cockpit instruments. 

With this setting, the altimeter indicates pressure altitude. Flight levels express that standard-pressure indication in hundreds of feet. At FL105, the altimeter reads 10,500 ft with standard pressure set. This does not necessarily mean the aircraft is 10,500 ft above mean sea level.

The practical purpose is consistency. Aircraft using flight levels share the same pressure reference, rather than using different local QNH settings.

Pressure Altitude vs Density Altitude

Pressure altitude also appears in performance questions, where temperature adds another consideration. This brings us to density altitude.

Pressure altitude identifies the altitude in the standard atmosphere corresponding to the measured pressure. Density altitude identifies the altitude corresponding to the actual air density. 

For typical ATPL calculations, density altitude is pressure altitude corrected for non-standard temperature. At a given pressure altitude, warmer air means higher density altitude, generally increasing take-off distance and reducing climb performance.

On a hot day at a high aerodrome, the aircraft may perform as though it were at a much higher elevation. Density altitude describes those conditions; it is not another altimeter setting or a measure of true altitude.

Exam reminder: Setting 1013.25 hPa gives pressure altitude. Density altitude requires a further calculation; it is not another pressure setting.

From Altitude to Flight Level

Knowing what each setting means is the first step. The next is understanding when pilots switch between the local QNH reference and standard pressure.

Three terms describe the changeover:

Climbing through TA, pilots change from QNH to SPS. Descending through TL, they change back to QNH. Within the transition layer, climbing aircraft therefore use flight levels and descending aircraft use altitudes.

The transition altitude is published for the relevant aerodrome or area. The transition level depends on the applicable transition altitude and pressure conditions, so it can change with QNH. Check the published procedures and the transition level provided through ATIS or ATC.

Pilot reminder: Changing the setting changes the indication, not the aircraft’s actual position. A jump in the displayed number is not a sudden climb or descent.

Pressure and Temperature

Why the indication can mislead

Choosing the correct setting establishes the reference. However, understanding the indication also means recognising how pressure changes and non-standard temperatures affect it.

Pressure: Changing the Setting vs Changing Location

First, consider an aircraft whose actual position stays unchanged. Increasing the pressure setting increases the indicated altitude; decreasing the setting decreases it.

Changing from 1000 to 1010 hPa, for example, raises the reading by approximately 300 ft, using 30 ft/hPa. The aircraft has not moved. Only its displayed reference has changed.

Now consider flying into an area of lower pressure without updating the setting. If you maintain the same indicated altitude, your true altitude decreases. The altimeter is now overreading because its setting is too high for the local pressure.

This is the situation behind “High to low, look out below.” Flying from higher to lower pressure without resetting can leave you lower than you think.

Exam tip: Before answering a question, distinguish between turning the subscale knob and flying into different pressure conditions.

Temperature: Why Correct QNH is Not Enough

Correct QNH does not remove temperature error. The altimeter still assumes standard atmospheric conditions when converting pressure into altitude.

In colder-than-standard air, pressure levels are closer together. Above the QNH reference elevation, the aircraft’s true altitude is lower than indicated. In warmer-than-standard air, the opposite applies.

The error grows with height above that reference and matters for terrain clearance. In temperature-correction questions, use the relevant height above the reference elevation, not automatically the entire altitude above MSL.

ATPL Worked Example

Let’s put the pressure-setting logic into practice. This question looks like a straightforward climb-time calculation, but the departure elevation and target flight level use different references.

Question: The elevation of the departure airport is 2,500 ft. An aircraft has to climb to FL105 at 750 ft/min. The QNH is 995 hPa. Determine the climb time.

1. Find the pressure difference. FL105 means an indication of 10,500 ft with standard pressure set. Before comparing it with aerodrome elevation, we need to account for the QNH.

Using 1013 hPa for standard pressure and 30 ft per hPa:

• Pressure difference = 1013 − 995 = 18 hPa

• Pressure correction = 18 × 30 = 540 ft

2. Put the target level on the QNH reference. QNH is lower than standard pressure. Changing the setting from 1013 to 995 hPa would therefore reduce the indication by approximately 540 ft.

At FL105, the corresponding indication with QNH set would be: 

10,500 − 540 = 9,960 ft

This gives us a target altitude on the same reference as the departure elevation.

3. Calculate the climb required. Now subtract the aerodrome elevation:

9,960 − 2,500 = 7,460 ft

This is the climb required under the question’s simplified assumptions. Subtracting 2,500 ft directly from 10,500 ft would miss the pressure correction.

4. Divide by the rate of climb. Using the given constant rate of 750 ft/min:

Climb time = 7,460 ÷ 750 = 9.95 minutes

That is approximately 9 minutes 57 seconds, or 10 minutes to the nearest minute.

Exam tips: check the reference and the sign. At the same aircraft position, compare the indication with QNH set against the pressure-altitude indication with standard pressure set:

• QNH above standard: the QNH indication is higher.

• QNH below standard: the QNH indication is lower.

Here, 995 hPa is below standard, so the QNH indication must be lower than 10,500 ft. That quick check confirms we should subtract the correction. No wind or airspeed calculation is needed. Once both levels share the same reference, divide the required climb by the given rate.

Common ATPL Questions and Traps

Altimetry questions become easier when you separate three things: the reference, the pressure setting and what the question asks you to find. Use these checks to spot the misunderstanding behind an answer, rather than memorising another set of formulas. 

• Flight level or true altitude? A flight level is a pressure reference. Before subtracting aerodrome elevation, put both values on the same reference.

• Reading change or actual movement? Resetting changes the indication without moving the aircraft. Check whether the question asks what the instrument shows or where the aircraft is.

• Which conversion factor? Use 27 ft/hPa or 8 m/hPa when explicitly specified, rather than automatically applying 30 ft/hPa.

• QFE or terrain clearance? QFE references a fixed aerodrome datum. For QNH–QFE conversions, you need its elevation: above sea level, QNH exceeds QFE; at sea level, they are equal.

• Pressure or temperature correction? Correct QNH does not eliminate cold-air error. Temperature matters for true-altitude and density-altitude calculations, but not a simple subscale change.

• True or density altitude? True altitude describes position above MSL. Density altitude describes air density in standard-atmosphere terms and helps assess performance.

• TA or TL? Think direction: change to SPS climbing through TA; change to QNH descending through TL.

Two other distinctions can appear in Meteorology questions. QFF, unlike QNH, reduces pressure to sea level using actual temperature conditions. In the usual comparison at an aerodrome above MSL, warmer-than-standard conditions give QNH greater than QFF.

The pressure group in a standard European METAR reports QNH, rounded down to the nearest whole hectopascal. For example, 1016.8 hPa becomes Q1016.

Further Reading

Want to connect the pressure settings with the instruments you’ll use? These guides explain what happens behind the reading and where to find it in the cockpit.

PFD Explained: The Screen Pilots Actually Fly – Find the altitude tape, vertical speed indication and pressure setting on an Airbus-style display.

Six-Pack Basics: Your Guide to Primary Flight Instruments – Review the altimeter alongside the other primary instruments and understand what each tells you.

Pitot Tube 101: How Your Airspeed Indicator Works – Explore static and pitot pressure to understand how pressure measurements become cockpit indications.

Altimeter Settings: Quick Reference

Use this table for a final check before tackling an altimetry question.

Calculation check: Put both levels on the same reference, use the stated conversion factor, and check the correction’s direction. Then decide what the question asks you to find. A quick higher-or-lower check can catch a sign error before it becomes your answer.

Keep Practising

One small detail, the reference behind the reading, can change your answer. Put what you’ve learnt into practice with altimetry questions in the Airhead ATPL Question Bank, while the logic is still fresh.