True Altitude Calculator

Why This Matters to Pilots

An altimeter is calibrated for the standard atmosphere. When the air is colder than standard, the true altitude is lower than what the altimeter indicates — the aircraft is closer to terrain and obstacles than the instrument suggests. The error grows with height above the reporting station and with colder temperatures.

This is why the FAA has published mandatory cold temperature altitude corrections at many airports. On an instrument approach with published corrections, always apply those corrections to the charted altitudes rather than relying on an estimate.

Limitations

• This is a planning estimate. It assumes the standard atmospheric lapse rate between the reporting station and your altitude; real temperature profiles (inversions, non-standard layers) will differ.
• It assumes the altimeter is set to the local altimeter setting so the indicated altitude already reflects local pressure. It does not correct for pressure errors or instrument error beyond any value you enter.
• On instrument approaches with published cold temperature corrections, apply the published corrections — not this estimate.

Reference: AIM 7-2-3 (Altimeter Errors) and FAA AC 91-105 (Cold Temperature Altitude Corrections).