QNH
Altimeter setting in hPa referenced to sea level
Last updated: April 20, 2026 · Maintained by Aviatr Editorial Team
What is QNH?
QNH is the altimeter setting that makes the aircraft altimeter read the airport elevation above mean sea level when on the ground. Set to the local QNH, the altimeter reads true altitude above sea level — the reference used for terrain clearance below the transition altitude in EASA airspace.
How is QNH used?
Pilots receive the local QNH from ATIS, tower, or the METAR before takeoff and on descent into an airport. Europe uses hectopascals (hPa); the US uses inches of mercury (inHg). A typical European QNH is 1013 hPa (standard) with realistic daily values between 990 and 1035 hPa. Correct QNH setting is critical because a one-hPa error introduces roughly 28 feet of altitude error — enough to matter on precision instrument approaches. Above the transition altitude (typically 3,000 to 18,000 feet depending on country and airspace) pilots switch to standard pressure 1013 hPa and fly flight levels. On descent back below the transition level, pilots reset to local QNH. Forgetting this transition is a common cause of terrain-clearance errors in initial instrument training and a recurring cause of controlled-flight-into-terrain events worldwide. Automated transitions between QNH and standard pressure now feature in most modern glass-cockpit avionics, reducing but not eliminating the human-factor risk of a missed reset.