Pressure altitude calculator
Altitude above the standard datum plane — what your altimeter reads with 29.92 set, and the input to almost every performance chart.
How it works
Pressure altitude = field elevation + (29.92 − altimeter setting) × 1,000.
Each 0.01 inHg is worth about 10 ft, and each hectopascal about 27 ft. When the pressure is lower than standard, pressure altitude is higher than your true elevation — which is the direction that hurts performance.
Why performance charts want it
An aircraft does not care about height above the sea. It cares about the density of the air going through the propeller and over the wing, and pressure altitude is the first half of that story — temperature, via density altitude, is the second.
The other reason it matters
Flying from high pressure to low pressure without resetting the altimeter leaves you lower than indicated. "High to low, look out below" is the mnemonic, and it is worth keeping because the error is in the dangerous direction.
Live: the lowest pressure being reported right now
Low pressure means pressure altitude sits above true elevation — the direction that costs you performance and, if you forget to reset, terrain clearance.
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For planning and study, not for operational use. Aircraft performance comes from your POH, not from a generic formula.