Cold Temperature Altimeter Error and Altitude Correction Calculator

This calculator estimates that effect from the indicated altitude, aerodrome elevation, and outside air temperature at the altimeter-setting source. It returns the signed altimeter error, estimated true altitude, and the positive correction to add when conditions are colder than ISA. The result supports approach planning and cross-checking, but it does not replace an approved cold-temperature correction table, procedure note, operator manual, or air traffic control requirement.

Enter the altitude and reference elevation consistently

Use the published uncorrected indicated altitude for the approach fix or terrain-clearance constraint as indicated_altitude_ft. Enter the elevation of the aerodrome or the location that supplies the altimeter setting as aerodrome_elevation_ft. Both values must use feet above mean sea level, and the indicated altitude must not be below the reference elevation. The calculator first subtracts the elevation to obtain height above the altimeter-setting source, because cold-temperature error grows with vertical separation rather than with altitude alone. Finally, enter the outside air temperature reported at that source in degrees Celsius. Do not enter a forecast temperature aloft or a cockpit total-air-temperature indication. Keeping the altitude datum, temperature location, and altimeter-setting source aligned is essential: mixing an airport elevation with a temperature from a distant station can produce a plausible-looking correction that does not represent the pressure column affecting the approach. For operational use, always select the values and rounding method required by the controlling procedure or authority.

Understand the sign and the correction

The calculation derives ISA temperature at the aerodrome elevation using the standard tropospheric lapse rate. It then compares actual temperature in kelvins with that ISA value and scales the indicated height above the aerodrome. In colder-than-ISA conditions, the estimated true height is smaller than the indicated height: the aircraft is lower than the altimeter suggests. The returned altimeter_error_ft is signed as true altitude minus indicated altitude, so a negative number means true altitude is lower. The cold_correction_to_add_ft field expresses the same cold effect as a positive amount suitable for adding to an indicated constraint. corrected_indicated_altitude_ft is the original indicated altitude plus that amount. In warmer conditions, estimated true altitude can be higher and the signed error becomes positive, but the cold correction is zero because this tool never recommends subtracting altitude for terrain clearance. Values are rounded for readable output only after the full-precision calculation, keeping all result fields internally consistent.

Use the estimate as a planning cross-check

Cold-temperature correction is a safety-critical operational subject, and published methods may use conservative tables, segmented corrections, temperature applicability limits, or special rules for minimum vectoring altitudes and missed approaches. This calculator provides a transparent analytic estimate, not an authorization to alter a clearance. Compare its result with the applicable aviation authority material, chart annotations, operator procedures, and any correction supplied by avionics. Apply corrections only to the fixes and altitude types covered by those instructions, and communicate corrected altitudes to air traffic control whenever the governing rules require it. Remember that obstacle clearance depends on more than temperature: pressure-setting errors, terrain data, navigation performance, wind, procedure design, and local restrictions remain relevant. The estimate is most useful for training, preflight planning, independent arithmetic checks, and understanding why the correction increases with colder temperature or greater height above the aerodrome. If the published table and this estimate differ, use the approved published value and its prescribed rounding direction.