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Lapse Rate Temperature Calculator

Enter the base temperature, altitude gain, and lapse rate to find the temperature at altitude.

How it is calculated

A straight-line estimate. drop (°C) = lapse rate (°C/km) × height gain (m) / 1000, then Ttop = Tbase - drop. The Fahrenheit value is Ttop × 9/5 + 32. Temperatures go in degrees Celsius and the height in metres, and the number you type is the height above the place where the base temperature was measured, not height above sea level. If the lapse rate is left empty the tool uses 6.5 °C per km. Height cannot be negative, so the tool cannot estimate warmer air in a valley below the base point. The rate is constant over the whole climb, with no allowance for inversions, humidity or time of day; use a larger rate, near 9.8, for dry air and a smaller one for saturated air.

Worked example

It is 18 °C at the trailhead and the summit is 1,800 m higher, using the default rate of 6.5 °C per km. Drop: 6.5 × 1800 / 1000 = 11.70 °C. Summit temperature: 18 - 11.70 = 6.30 °C. In Fahrenheit: 6.30 × 9/5 + 32 = 43.34 °F. With the dry rate of 9.8 the drop would be 17.64 °C and the summit would be only 0.36 °C.

Try this example →

Common mistakes

  • Entering the summit's altitude above sea level instead of the climb from where the base temperature was taken; a town at 800 m with a peak at 2,600 m needs 1,800.
  • Typing the lapse rate per metre (0.0065) rather than per kilometre (6.5), which makes the drop almost zero.
  • Entering the base temperature in Fahrenheit; the input is Celsius, and the Fahrenheit figure is only an extra output.
  • Using the standard 6.5 rate on a day with a temperature inversion or in dry desert air, where the true rate can be quite different.
  • Treating the answer as a forecast for the exact summit; wind, sun and cloud on the day can shift the real temperature well away from this estimate.

About this calculator

As air rises through the atmosphere it expands and cools, a relationship meteorologists describe with the environmental lapse rate — the rate at which temperature drops with altitude. The often-cited standard atmosphere value is about 6.5°C per kilometre, though the actual rate varies with humidity and weather: dry (unsaturated) air cools faster, near the dry adiabatic lapse rate of roughly 9.8°C/km, while saturated air cools more slowly because condensation releases latent heat.

This calculator applies a chosen lapse rate to a base temperature and an altitude gain to estimate the temperature higher up. It’s used by pilots and meteorologists forecasting conditions aloft, by mountaineers and hikers anticipating how cold it will get on a summit, and by engineers doing rough atmospheric and HVAC calculations where elevation changes matter.

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  • Editorial team

    The default 6.5 is an average for free air, but a mountain day can differ. With a base of 15 degrees and a 1000 m climb, the default gives 8.50 degrees while the dry rate of 9.8 gives 5.20. Cold air pooling in a valley can also make the base itself unusually low. Post the base and summit temperatures you actually measured and the lapse rate that matched.

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