Temperature at Altitude Calculator

Air temperature generally decreases with height through the troposphere because rising air expands as atmospheric pressure falls. The International Standard Atmosphere represents this change with a standard lapse rate of 6.5 degrees Celsius per kilometre, or 0.0065 degree per metre. This calculator subtracts that standard decrease from a chosen sea-level reference temperature and reports the result in Celsius, Fahrenheit, and Kelvin. It accepts altitude in metres or feet and a reference temperature in Celsius or Fahrenheit. With the ISA sea-level temperature of 15 degrees Celsius, the model gives 8.5 degrees at 1,000 metres and minus 17.5 degrees at 5,000 metres. The relationship is linear within the lower standard atmosphere: temperature equals base temperature minus lapse rate times altitude in metres. Fahrenheit input is converted to Celsius before the lapse rate is applied, while feet are converted using 0.3048 metre per foot. The final temperature conversions are performed only after the atmospheric calculation. This is a standard-model estimate, not a weather forecast. Actual temperature profiles vary with season, latitude, time of day, air mass, cloud, humidity, and local terrain. Temperature inversions can make air warmer with height, while dry and saturated rising parcels follow different adiabatic lapse rates. Mountain summit temperatures can differ considerably from the value estimated from a distant lowland station. Use current observations and an aviation weather briefing whenever safety or operational decisions depend on atmospheric conditions. The constant 6.5-degree lapse rate is intended for the tropospheric portion of the ISA, extending to about 11 kilometres or 36,000 feet. Above the tropopause, the standard atmosphere uses different layers and the simple linear rule no longer applies. Even below that boundary, a custom measured base temperature improves relevance but does not capture changing lapse rates along the route. The calculator is useful for classroom physics, rough hiking preparation, aviation exercises, meteorology demonstrations, and quick comparisons between elevations. Keep altitude referenced consistently to mean sea level, and distinguish environmental lapse rate from temperature changes experienced by an individual moving air parcel.