acronym for standard pressure (1013.2 hectopascals) measured at mean sea level at one atmosphere. Used as an altimeter setting. Area QNH refers to a reference pressure setting applicable for all aviation activities in a particular area.
The current barometric pressure setting adjusted for the height of that airfield above sea level. In other words, an altimeter set to the QNH figure for that airfield would indicate the actual height of the airfield above sea level when the aircraft was on the runway. It would appear that the meaning of the N in QNH has been lost throughout the ages. [Q N Height
Altimeter setting to obtain aerodrome elevation when on the ground
QNH is a Q code. It is a pressure setting used by pilots, air traffic control (ATC) and low frequency weather beacons to refer to the barometric altimeter setting which will cause the altimeter to read altitude above mean sea level within a certain defined region. This region may be fairly widespread, or apply only to the airfield for which the QNH was given.