True Altitude Calculator
Estimate your true altitude by correcting indicated altitude for non-standard temperature. Cold air makes an altimeter over-read, so on a cold day your true altitude is lower than indicated — an important terrain-clearance consideration.
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).
Related Calculators
Frequently Asked Questions
This calculator is for educational and planning purposes only. Always refer to your aircraft's POH/AFM, current NOTAMs, and official weather briefings. No calculator is a substitute for pilot-in-command judgment or CFI guidance. Read our full Safety Disclaimer.
True Altitude in Depth
True altitude is your actual height above mean sea level, as opposed to the indicated altitude your altimeter displays. On a standard day the two agree, but when the air is colder than standard the altimeter over-reads, placing you lower than indicated — a subtle error that becomes a serious terrain and obstacle-clearance concern in cold weather and mountainous terrain.
This is the physical basis for the aviation adage "from high to low or hot to cold, look out below." The altimeter assumes a standard temperature profile; when reality is colder, the column of air is more compressed, and your true height is less than the instrument suggests. Understanding and correcting for this protects your margins on instrument approaches and low-altitude operations in winter.
Step-by-Step: How the Calculation Works
The calculator applies a temperature correction to indicated altitude based on the difference between the actual temperature and the standard temperature for that altitude, referenced to the height above the reporting station. The colder the air relative to standard, the larger the downward correction to find true altitude. The FAA publishes a cold-temperature correction table and identifies specific airports where these corrections are mandatory on instrument procedures.
For planning, the correction grows with both the temperature deviation and the height above the altimeter source, so a cold day combined with a high approach segment produces the largest errors. This tool implements the standard correction consistent with AIM guidance and FAA Advisory Circular 91-105 so that student and instrument pilots can see how significant the effect becomes.
More Worked Examples
Example 1 — Cold-weather approach
Indicated altitude 3,000 ft above a reporting station, temperature 30 degrees Celsius colder than standard. The correction can exceed 300 feet, meaning your true altitude is nearer 2,700 ft — a meaningful loss of obstacle clearance on a non-precision approach.
Example 2 — Mild deviation
The same 3,000 ft indicated but only 10 degrees colder than standard yields roughly a 100-foot correction, illustrating how the error scales with the temperature deviation.
Pilot Decision-Making Context
True altitude corrections directly affect the safety of instrument approaches, minimum en route altitudes, and low-level operations in cold climates. When flying in very cold conditions, pilots add the published cold-temperature corrections to minimum altitudes to preserve obstacle clearance, and at designated cold-temperature-restricted airports these corrections are required.
Even under visual flight rules, being aware that a cold day places you lower than indicated encourages a conservative approach to terrain and obstacle clearance. The habit of thinking about true altitude, not just indicated altitude, is a hallmark of a careful cold-weather pilot.
More Questions Answered
When are cold-temperature corrections required?
The FAA designates certain airports where cold-temperature altitude corrections must be applied to instrument approach segments when the temperature is at or below a published threshold. Outside those, corrections are strongly recommended in very cold conditions.
Does a warm day cause the opposite error?
Yes. When the air is warmer than standard, the altimeter under-reads and your true altitude is higher than indicated. This is generally less hazardous for terrain clearance but still relevant for accurate altitude keeping.
Do I correct for temperature under normal conditions?
For everyday operations near standard temperatures the error is small and usually ignored. It becomes important in significantly colder-than-standard air, especially at height above the altimeter setting source.
Related Reading & Tools
Want AI explanations, checkride questions, and saved calculations?
FlightCalculators.com is powered by the same team behind SkeyeMentor — the AI-powered FAA ground school. Try SkeyeMentor free.
Try SkeyeMentor Free