Altimeter setting and pressure altitude

1Select airport field elevation, ft MSL

2Aircraft position

3Current atmospheric conditions

30.21inHg
Local altimeter setting (reported by ATIS/AWOS)

4Kollsman window setting

Feet MSL Sea level (0 ft MSL) Height above the selected airport's field elevation (its reference elevation), not necessarily the height above the terrain below the airplane. Height above airport0 ftfrom field elevation, not terrain 29.92 inHg pressure surface True altitude9 ft MSL Pressure altitude (ft) 0 ft 29.92 ALT 100 FEET
Indicated Altitude
9 ft
Calculated Pressure Altitude
9 ft
True Altitude (MSL)
9 ft
Estimated Pressure Altitude (1,000-ft Rule)
9 ft

How we calculate pressure altitude

Pressure altitude ≈ Field elevation + [(29.92 − Local altimeter setting) × 1,000]1,000-ft rule

Another way: set 29.92 in the Kollsman window. The altimeter then reads pressure altitude.

Why it matters: POH performance charts are entered with pressure altitude. Lower generally helps, but temperature still decides density altitude. The Kollsman window changes only the reading.