What is QNH?

QNH is the altimeter pressure setting that makes the altimeter read height above mean sea level, so it shows the aerodrome's elevation when you are on the ground.

QNH is a pressure setting fed into the altimeter's subscale. Set it, and the altimeter reads altitude above mean sea level (AMSL). On the ground at the aerodrome, the altimeter will therefore read the aerodrome's elevation.

QNH is the setting used for most flying below the transition altitude and for terrain and obstacle clearance. It is given in the METAR (for example Q1021 means 1021 hectopascals) and passed by ATC.