Why does ATC give an altimeter setting and how do I use it?
Learn why ATC gives QNH, how to set the altimeter in MSFS 2024, convert hPa to inHg, and when to use 29.92 or 1013.
ATC gives an altimeter setting so every aircraft in the area uses the same local pressure reference. Set the issued QNH or altimeter value in the barometric window below the applicable transition boundary; use standard 29.92 inHg/1013.25 hPa for flight levels. In Microsoft Flight Simulator 2024, adjust the cockpit’s BARO control.
Why does the ATC altimeter setting matter?
ATC issues a local setting because atmospheric pressure changes with weather, time and location, causing an unchanged altimeter setting to become inaccurate. When nearby aircraft use the same pressure reference, their indicated altitudes remain comparable for vertical separation, approaches and terrain-clearance procedures.
The value is usually QNH, or an operationally equivalent local altimeter setting, derived from a reporting station and reduced to mean sea level. With QNH selected, the altimeter indicates approximately altitude above mean sea level and should show roughly the published airfield elevation while parked there. Our explanation of how QNH turns station pressure into an altitude reference covers the underlying pressure reference.
If the selected setting is too high, the altimeter indicates too high and the aircraft is lower than it appears. A correct pressure setting does not remove every error: unusually cold air can also make true altitude lower than indicated, which is why some real-world procedures require cold-temperature corrections.
How do I set the altimeter in MSFS 2024?
To set the altimeter in Microsoft Flight Simulator 2024, copy the pressure from ATC or ATIS, select the correct units and adjust the aircraft’s BARO control until that value appears.
- Copy the complete setting. US-style ATC may say “altimeter two niner eight five”, meaning
29.85 inHg. Elsewhere, “QNH one zero one five” means1015 hPa. METAR pressure groups may appear asA2985orQ1015. - Decide whether local pressure or standard is required. Use the local setting while operating on altitudes below the applicable transition boundary. If ATC gives QNH while you are still flying a flight level, copy it but wait until the prescribed descent changeover point before selecting it.
- Check the pressure units. Look for
IN,IN HG,HPAorMB. Hectopascals and millibars have the same numerical value. Change the cockpit’s unit option or convert the number; never enter29.85into an hPa display. - Adjust the BARO control. Mechanical altimeters use a barometric or Kollsman window. Glass cockpits usually show the setting beside the altitude tape, with the control on the PFD or EFIS panel. If
STDis displayed, return the instrument to local-pressure mode first. The exact push, pull or click action varies by aircraft. - Set every independent instrument. Check the captain’s, first officer’s and standby altimeters where they have separate controls. A common simulator mistake is correcting the primary display while leaving the standby instrument on standard pressure.
- Cross-check the indication. On the reporting airfield, QNH should produce approximately the published field elevation rather than zero. A large error points to wrong units, QFE, stale simulator weather, an instrument failure or the wrong airport’s pressure.
MSFS 2024 also provides assignable altimeter controls. Search the simulator’s control bindings for the altimeter-setting command rather than assuming a particular keyboard or controller button, because profiles and platforms differ. An automatic setting command may use the pressure loaded by the simulator’s weather system, which can disagree with a value just spoken by built-in ATC.
How do I convert QNH to inHg?
To express QNH in inHg, multiply the hPa value by 0.02953; to convert inHg to hPa, multiply by 33.8639. Use the issued units directly whenever the cockpit supports them, since display rounding can introduce a small difference.
| Issued value | Equivalent setting | How to interpret it |
|---|---|---|
QNH 1015 | About 29.97 inHg | Set 1015 hPa, or 29.97 if the instrument accepts only inHg |
QNH 1013 | About 29.91 inHg | A local QNH of 1013; it is not automatically an instruction to select STD |
STD | 1013.25 hPa or 29.92 inHg | Standard pressure used for flight levels |
29.85 inHg | About 1011 hPa | Enter 29.85 on an inHg display or approximately 1011 on an hPa-only instrument |
QNH 1013 deserves care. If ATC explicitly says QNH 1013, it is the local setting for altitude operations. Standard pressure is precisely 1013.25 hPa and is normally selected as STD; the numerical difference is small, but the procedural distinction between altitude and flight level remains.
When should I use QNH instead of 29.92 or 1013?
Use local QNH for indicated altitudes near departure and arrival, and use standard 29.92 inHg or 1013.25 hPa when operating on flight levels above the applicable transition boundary.
| Pressure reference | Normal use | Altimeter indication |
|---|---|---|
| Local QNH or altimeter setting | Below the transition altitude on climb and below the transition level on descent | Approximate altitude above mean sea level |
| Standard pressure | Above the transition altitude on climb and until the transition level on descent | Pressure altitude expressed as a flight level |
| QFE | Only where explicitly issued or required | Approximate height above the nominated airfield datum, often near zero on the ground |
Transition altitudes and levels vary by country and airport. Do not assume one universal changeover height. See our guide to why 29.92 is used for flight levels and the practical climb-and-descent altimeter changeover sequence for the phase-of-flight details.
What is an altimeter setting region?
An altimeter setting region is airspace where aircraft use current station altimeter settings under that region’s rules, rather than standard pressure being used throughout. The term is particularly prominent in Canadian procedures, which distinguish altimeter-setting regions from standard-pressure regions.
This describes a geographic operating procedure, not the cockpit’s inHg/hPa selector. Follow the applicable charts and ATC instructions because simulator ATC may simplify regional altimeter rules.
Does turning the altimeter setting up make altitude go up?
Yes: with the aircraft at the same height, increasing the selected pressure makes the indicated altitude rise. The useful cockpit rule is “pressure up, indicated altitude up”.
Near sea level, changing the setting by 0.01 inHg changes the indication by roughly 10 feet; 0.10 inHg is about 100 feet. One hPa is approximately 27 feet, so a 4 hPa error is a little over 100 feet. These are practical approximations, not exact corrections for every altitude and temperature.
Why does QNH show only approximately the airport elevation?
QNH should place the altimeter near the published elevation, but it is still a pressure instrument rather than a direct terrain-height sensor. Instrument tolerances, pressure gradients, temperature, a reporting station away from the runway and simulator scenery or weather mismatches can all create a modest difference.
A large discrepancy is not normal. An altimeter showing near zero at an elevated airport probably has QFE selected; one showing an unexpectedly high value may still be in STD mode or have an incorrect unit conversion.
What if ATC’s setting does not match the weather or altimeter?
Confirm the station, observation time, units and pressure reference before changing anything. In real-world flying or with human ATC, query an unexplained discrepancy rather than silently substituting another number.
In an offline simulator, built-in ATC, airport weather displays and the active weather model can fall out of synchronisation. For an approach, verify the pressure associated with the weather actually loaded at the destination and check that the altimeter agrees approximately with runway elevation. Do not continue an unsafe descent merely to satisfy simulator ATC.
STDremains selected below the transition level.- InHg has been entered as hPa, or hPa as inHg.
- QFE has been mistaken for QNH.
- The pressure came from another airport or an older observation.
- Only one of several altimeters was adjusted.
- A simulated static-system or instrument failure is active.
- GPS altitude is being compared directly with barometric altitude; they use different measurement methods and need not match exactly.
If the error remains after these checks, use our diagnostic guide to a wrong simulator altimeter reading to isolate weather, pressure-reference and instrument problems.