Pressure Altitude Calculator
Convert field elevation and altimeter setting into pressure altitude.
Inputs
Result
Pressure altitude
1,308ft
Altitude in the standard atmosphere
Altimeter correction
Low pressure — PA above field elevation
+308ft
Pressure altitude 1,308 ft (+308 ft correction)
Formula
Ref- PA = elevation + (1013.25 − QNH_hPa) × 30 [ft]
- inHg is converted to hPa first (1 inHg = 33.8639 hPa)
Worked example
RefField elevation 1,000 ft, QNH 1003 hPa.
- 1.Pressure difference = 1013.25 − 1003 = 10.25 hPa (low pressure).
- 2.Correction = 10.25 × 30 = +308 ft.
- 3.PA = 1,000 + 308 = 1,308 ft.
Pressure altitude ≈ 1,308 ft.
How it works
RefPressure altitude is what the altimeter reads with 1013.25 hPa (29.92 inHg) set — the reference for flight levels and for every performance chart. Below standard pressure the pressure altitude sits above the field; above standard it sits below. Whether you enter the setting in hPa or inHg, it is normalised to hPa first so both give the same answer.
DGCA student tip
Exam‘High to low, look out below.’ When QNH is lower than standard, true altitude is lower than indicated — and pressure altitude is higher than field elevation. The 30 ft/hPa rule is the fast way to get there.
Common mistakes
Watch- Reversing the sign — low QNH increases pressure altitude, not decreases it.
- Forgetting to reset the subscale to 1013 hPa / 29.92 inHg before reading pressure altitude.
- Confusing pressure altitude with density altitude (temperature is not applied here).