How to use the altitude temperature calculator
- Enter the temperature and wind speed at the start and the summit altitude to get the expected summit temperature and wind chill. If you start above sea level, enter the start altitude too.
- Change the summit wind factor to 1.5 or 2 times to model a windy ridge.
- Use the clothing advice and the altitude table below the result to prepare your gear.
Why temperature falls as altitude rises
When air rises, the surrounding pressure falls and the air expands, using heat energy so that its temperature falls. This is called adiabatic expansion, where the temperature of the air parcel changes without heat moving in or out. Dry air in which no vapor condenses cools about 1 °C per 100 m, moist air forming cloud cools about 0.5 °C, and the real average sits between them at about 0.6 °C.
For example, on a day with 15 °C at sea level, a 1,200 m summit is expected to be 15 − (1,200 ÷ 100 × 0.6) = 7.8 °C. If wind of 18 km/h blows, the wind chill drops to about 5 °C. Weather that needed only light clothing on the flat becomes weather that needs warm gear at the summit.
Keeping warm in the mountains
Hypothermia occurs when the body loses heat faster than it makes it, and it can happen above freezing, not only in deep winter, if you are wet and exposed to wind. Clothing soaked with sweat takes heat away as it cools, so take off outer layers on climbs to reduce sweat and put them on right away when resting. Choose synthetic fabrics or wool that dry quickly over cotton for base layers.
To keep warm, wear several layers, bring windproof and waterproof outerwear, and pack gloves, a hat and spare socks. Eating high-energy trail food regularly and carrying a hot drink help. If shivering does not stop, speech becomes slurred or steps become unsteady, move to shelter from the wind at once, change into dry clothes and call emergency services.
Pre-hike checklist
- Check the mountain forecast and trail closures.
- Set a finish time before sunset and carry a headlamp.
- Pack spare warm clothing for rests at the summit.
- If rain is forecast, bring a waterproof jacket and a pack cover.
- If hiking alone, tell someone your route and expected return time.
FAQ
Does temperature really drop 0.6 °C per 100 m?
The average drop of about 0.5 to 0.65 °C per 100 m in moist air is called the lapse rate and 0.6 is the common value. It drops less with cloud or humidity and more when clear and dry. On some mornings with a temperature inversion it can even be warmer higher up.
How is wind chill calculated?
It uses the wind chill formula from Canadian and US weather agencies, which applies at 10 °C or below with wind of about 4.8 km/h or more. At the same air temperature, stronger wind lowers the felt temperature a lot. Humidity and sunshine are not included.
Why is summit wind adjusted separately?
Summits and ridges are often much windier than flat ground because of terrain. Using only the ground wind can underestimate the chill, so you can assume 1.5 or 2 times the wind at the summit. Check the official mountain forecast for real values.
Notes & limitations
This calculator is a reference tool using an average lapse rate and a wind chill formula, and it is not medical advice. Mountain weather can change quickly, so put forecasts and on-site conditions first and avoid risky hikes.