Temperature at altitude calculator

It applies the standard environmental lapse rate of 6.5 degrees Celsius per 1,000 meters of climb, or its equivalent for feet. Enter the target altitude and, when the observation was taken above sea level, the surface altitude as well. Results are available in Celsius, Fahrenheit, or Kelvin. The calculation is deterministic and useful for planning, comparison, and education, but it does not replace an aviation weather briefing or an actual airborne temperature observation.

Start with the right surface observation

Choose a surface air temperature that represents the place and time of the intended flight. A recent airport observation is usually more useful than a daytime high from a general forecast because temperature changes with hour, cloud cover, terrain, and passing weather systems. Enter that value in Celsius, Fahrenheit, or Kelvin, then select the matching temperature unit. The calculator treats the observation altitude as the starting point of the climb. If the observation comes from an airport at 1,500 meters above mean sea level, enter 1,500 as the surface altitude rather than leaving the default of zero. Enter the target flight altitude in the same altitude unit. The calculation uses the difference between the target and observation altitudes, not simply the target altitude itself. This distinction prevents the cooling already represented by a high-elevation surface reading from being counted twice. For a conservative operational decision, consult official aviation weather products and account for forecast changes rather than relying on one surface value alone.

Understand the standard lapse-rate calculation

In the lower atmosphere, air temperature often decreases as height increases. This estimator uses a fixed environmental lapse rate of 6.5 degrees Celsius for every 1,000 meters, equivalent to about 1.98 degrees Celsius per 1,000 feet. It converts the altitude difference to meters, multiplies that height by 0.0065 degrees Celsius per meter, and subtracts the resulting temperature change from the surface temperature. Celsius and Kelvin have equal-sized degrees, while Fahrenheit inputs and outputs are converted through Celsius so that the same physical change is applied correctly. The returned temperature change is expressed in degrees Celsius to make the applied model transparent, even when the selected output temperature is Fahrenheit or Kelvin. Values are rounded to two decimal places for stable, readable results. The method is deterministic: identical inputs always produce identical output. It does not introduce humidity, pressure, cloud layers, inversions, fronts, or changing lapse rates, all of which can make the real atmosphere depart substantially from this simplified profile.

Use the estimate within its limits

The result is best treated as a baseline estimate for trip planning, classroom exercises, equipment checks, or a quick reasonableness comparison with a forecast sounding. It can help a traveler anticipate that a warm departure airport may still correspond to freezing temperatures at altitude, or help a pilot compare a reported outside air temperature with a simple standard-rate expectation. However, the atmosphere does not cool at one constant rate everywhere. Temperature inversions can produce warming with height, saturated air cools at a different rate, and the tropopause eventually limits the simple linear relationship. Local terrain and weather systems can shift the profile further. Do not use this calculation as a substitute for official METARs, TAFs, winds-and-temperatures-aloft forecasts, pilot reports, aircraft instruments, or required preflight planning. The estimator also does not calculate density altitude, icing probability, cloud base, or aircraft performance. Those tasks depend on additional variables and dedicated methods. Through the API, each calculation costs $0.002; the same inputs make automated planning records easy to reproduce and audit.