When should pilots reset the altimeter setting?

Pilots reset the barometric altimeter whenever its required pressure reference changes: before take-off, when a revised local setting applies below the transition altitude, to standard pressure while climbing through that altitude, and back to local pressure while descending through the transition level. Charts, ATC and local procedures set the exact changeover.

What does an altimeter reset mean in aviation?

An aviation altimeter reset is a pressure-reference change, not an altitude reset, zeroing action or instrument calibration. Within our Aviation & Real-World Flying guidance, “reset” means turning the pressure-setting control or selecting STD so the barometric altimeter uses the correct reference.

With QNH or the applicable local altimeter setting selected, the instrument indicates altitude approximately above mean sea level. With standard pressure selected—1013.25 hPa or 29.92 inHg—it indicates pressure altitude and vertical position is reported as a flight level. Changing this setting does not alter the aircraft’s physical altitude, although the indicated altitude changes immediately.

A barometric reset does not reset GPS altitude or the radio altimeter. Those systems use different references.

What about QFE and other non-standard references?

QFE makes the altimeter indicate approximately zero at the aerodrome or another specified datum, so airborne indications represent height above that datum. It is used only where the published procedure or operator requires it; pilots must not substitute QFE for QNH by habit.

Any pressure reference other than 1013.25 hPa or 29.92 inHg is non-standard in the flight-level sense, but QNH remains the normal operational setting below the transition altitude in most regions.

When is each altimeter setting changed?

The correct setting follows the phase of flight and the vertical reference being used.

On the ground, QNH should produce a plausible indication close to the published aerodrome elevation. Do not turn the setting away from the reported value merely to force an exact match; a discrepancy outside the permitted tolerance may indicate the wrong pressure, wrong units, unsuitable weather data or an instrument fault.

At what altitude (vilken höjd) do pilots select standard pressure?

There is no worldwide reset altitude: pilots select standard pressure at the published transition altitude during the climb and restore local pressure at the applicable transition level during descent.

The transition altitude and transition level are not necessarily the same vertical point. A transition layer separates aircraft operating on local-pressure altitudes from those operating on standard-pressure flight levels. The transition altitude is often fixed for a country or aerodrome, while the transition level may change with QNH.

In the United States, 18,000 feet MSL is the usual boundary for selecting 29.92 inHg, although low pressure can make FL180 unavailable as the lowest usable flight level. Other countries and aerodromes use transition altitudes far below 18,000 feet. Never assume that 10,000 feet or 18,000 feet applies globally; use the chart, ATC instruction and applicable procedure. Our explanation of how transition altitude, transition level and the transition layer fit together covers that distinction in detail.

Crews may enter destination QNH into an arrival or performance page before reaching the transition level. That is preparation, not necessarily activation of the setting on the primary altimeter.

Should pilots reset the altimeter whenever ATC gives new pressure?

Pilots operating by altitude should apply a newly issued local setting promptly when it is the setting applicable to their position and clearance.

An aircraft operating at a flight level remains on standard pressure even if ATC or ATIS broadcasts a new surface setting. The crew may record or preselect the new QNH if the aircraft supports that function, but it is activated at the descent changeover point specified by the procedure.

Retaining stale QNH while flying from high pressure towards lower pressure makes the aircraft lower than the indicated altitude—the reason for the warning “high to low, look out below”. Near sea level, a difference of 1 hPa changes the indication by roughly 27 feet; 0.01 inHg is approximately 10 feet. For the operational reason behind these updates, see how to interpret and apply an ATC altimeter setting.

How should an altimeter reset be performed and checked?

A correct reset verifies the pressure source, operating regime, units and every altimeter that the crew relies upon.

1. Identify the required reference. Confirm whether the aircraft should be using an altitude on local pressure or a flight level on standard pressure. A clearance to a flight level does not normally mean selecting STD early while still below the transition altitude.
2. Obtain the applicable pressure. Use the latest setting supplied by ATC, ATIS, AWOS or another source approved for the operation. A nearby report is not automatically valid if a different regional setting has been assigned.
3. Check the units. Confirm whether the instrument expects hectopascals or inches of mercury. Standard pressure is 1013.25 hPa, commonly displayed as 1013, or 29.92 inHg.
4. Set every required instrument. Update both primary altimeters where fitted and the standby altimeter. Some aircraft provide a synchronisation function, but crews should still verify each display.
5. Confirm the annunciation. Check for the intended numerical value or STD indication and ensure the resulting altitude is plausible.
6. Cross-check the vertical reference. Make sure clearances, selected values and call-outs consistently use altitude or flight level after the change.

The indicated altitude will move when the pressure setting changes even though the aircraft has not instantly climbed or descended. How the autopilot reacts depends on the aircraft and its altitude-control system, so the change should be monitored rather than treated as a purely cosmetic display adjustment.

Which mistakes cause a wrong altitude after the reset?

Most incorrect indications come from choosing the wrong reference or pressure source rather than from a failed altimeter.

• Selecting STD automatically at 10,000 feet when the published transition altitude is elsewhere.
• Activating destination QNH at the start of descent while the aircraft is still operating at a flight level.
• Leaving departure QNH set after entering an area with substantially different pressure.
• Entering a hectopascal value while the control is set to inHg, or misreading a value such as 29.92.
• Changing one primary display while leaving the other or the standby altimeter on the old setting.
• Confusing QNH with QFE and creating an error approximately equal to the aerodrome elevation.
• Turning the pressure knob to compensate for cold temperature. Required temperature corrections are applied as the procedure directs; they do not replace the reported QNH.
• Comparing pressure altitude directly with GPS or radio-altimeter height and assuming that any difference means the barometric instrument is faulty.

Is the altimeter reset the same in real life and a flight simulator?

Yes—the pressure-setting logic is the same in real life and realistic simulation, but simulator weather sources, aircraft coding and automatic commands introduce extra failure points.

Use the pressure generated by the weather system that is actually controlling the simulated flight. An external weather report, the simulator’s ATIS and an add-on weather engine may disagree because they represent different data or update times.

A mistake we see constantly is using an automatic “set altimeter” command at every phase of flight. Depending on the simulator and aircraft, that command may select local pressure even though the aircraft should remain on STD at a flight level. Treat it as a convenience, then verify the setting and annunciation manually.

Complex add-on aircraft may have separate pressure controls for each primary display and the standby instrument. For a platform-specific example, our procedure for setting QNH and STD in Microsoft Flight Simulator 2024 shows the practical sequence. If the indication remains implausible, work through our guide to diagnosing a wrong flight-simulator altimeter reading, including stale weather, unit mismatches, QFE and scenery-elevation discrepancies.