Plain English Meaning

QNH is the local pressure number you put into your altimeter so it reads the airport's actual elevation when you're on the ground, and your real height above sea level when you're flying.

Full Definition

QNH is the local station pressure, corrected to mean sea level using the standard atmosphere, that a pilot dials into the altimeter's Kollsman window so the instrument indicates true elevation above sea level. When QNH is set correctly, an aircraft sitting on the airport ramp will display the published field elevation, and in flight the altimeter will indicate above mean sea level () referenced to local pressure .