How to Calculate the Temperature on a Summit | 0.6°C per 100 m, Feels-Like Temperature and What to Wear
Even on a day when a T-shirt feels right at the foot of the mountain, you can find yourself shivering in a cold wind at the summit. Weather forecasts usually give the temperature down in the valley, so you need to estimate the temperature higher up yourself. This article explains how to calculate it using the rule that the air gets about 0.6°C colder for every 100 m you climb, a rule of thumb for the feels-like temperature from the wind speed, worked examples at specific elevations, what to wear for each feels-like temperature, and the cases where the calculation does not hold.
The temperature drops about 0.6°C for every 100 m you climb
The higher you go, the lower the air pressure, so air expands and cools. On average, the temperature falls about 0.6°C for every 100 m of elevation. This rate of decrease is called the lapse rate, and it is the basis for estimating temperatures in the mountains.
For example, if a trailhead at 600 m is 20°C, a summit at 1,600 m is 1,000 m higher, which is ten steps of 100 m, so the guideline is 20 − 0.6 × 10 = 14°C. Remember that it is about 6°C colder for 1,000 m of elevation and about 12°C colder for 2,000 m, and you can estimate it in your head.
Worked examples by elevation
| Base elevation and temperature | Summit elevation | Difference | Summit temperature |
|---|---|---|---|
| 200 m, 25°C | 600 m | 400 m | About 22.6°C |
| 600 m, 20°C | 1,600 m | 1,000 m | About 14°C |
| 500 m, 28°C | 2,000 m | 1,500 m | About 19°C |
| 1,500 m, 25°C | 2,900 m | 1,400 m | About 16.6°C |
| 2,300 m, 15°C | 3,000 m | 700 m | About 10.8°C |
| 0 m (seaside), 30°C | 3,776 m (Mount Fuji) | 3,776 m | About 7.3°C |
| 0 m (seaside), 20°C | 3,776 m (Mount Fuji) | 3,776 m | About −2.7°C |
Even when it is 30°C at the seaside in midsummer, the calculation puts the summit of Mount Fuji at only about 7°C. On a spring or autumn day when the seaside is 20°C, the summit works out below freezing. Even on a low mountain, a few hundred metres of climbing means a few degrees colder, so do not choose your clothing from the temperature at the bottom alone.
You can find the base temperature from the forecast for an observation point near the trailhead, or from a mountain weather forecast service. If you know the elevation of the observation point, use it as the base elevation in the calculation.
Each 1 m/s of wind makes it feel about 1°C colder
With nothing to block it, the wind on a mountain tends to be stronger than at the foot. Wind strips heat from the surface of your body, so it feels colder than the actual temperature. In hiking, a common rule of thumb is that each 1 m/s of wind lowers the feels-like temperature by about 1°C.
| Summit temperature | Wind speed | Approximate feels-like temperature |
|---|---|---|
| 14°C | 5 m/s | About 9°C |
| 19°C | 5 m/s | About 14°C |
| 16.6°C | 8 m/s | About 8.6°C |
| 10.8°C | 10 m/s | About 0.8°C |
| 7.3°C | 8 m/s | About −0.7°C |
A 10 m/s wind is strong enough to make you sway when you stand. Even if the summit is 10°C, in a wind like that it feels like around 0°C. On routes with long stretches along a ridge, expect to get just as cold on the ridge as on the summit. How walking and your body are affected at each wind speed is covered in the wind speed guide.
What to wear for each feels-like temperature
| Feels-like temperature at the summit | What to wear |
|---|---|
| 20°C and above | Short sleeves are fine for walking. Choose a synthetic or wool base layer that does not chill you when sweaty. Watch out for sun and heatstroke, and carry extra water |
| 10–20°C | Long sleeves plus a light jacket. Hot when walking, cold when you stop. Keep a wind shell or rain jacket ready to put on |
| 5–10°C | Add an insulating layer (fleece or light down). You cool down fast at breaks and on the summit, so a hat and gloves are reassuring |
| 0–5°C | Down jacket, gloves and a knit hat. Being wet with sweat brings a risk of hypothermia. Always carry a windproof jacket |
| Below 0°C | Below freezing. Ice and snow are possible and winter gear is needed. Summer gear alone is dangerous |
- Avoid cotton base layers; choose synthetic or wool layers that dry quickly
- A rain jacket is useful not only in rain but also as a windbreaker
- Wear thin layers you can add or remove to adjust
- If the feels-like temperature is likely to be around 0°C, consider changing the plan itself
On cold days your body uses more energy to stay warm, so take extra trail food (how to decide how much trail food to bring). On hot days you sweat more, so take extra water (the water amount article).
When the calculation does not hold
The figure of 0.6°C is an average, and the actual rate of cooling depends on the weather. On a clear day with dry air it can approach 1°C per 100 m, while inside cloud or in rain it may be only about 0.5°C.
- On clear mornings, radiative cooling can make valleys and basins colder, so the temperature may not drop as you climb (a temperature inversion)
- In strong sunshine it can feel warm even when the air temperature is low
- Inside cloud or fog there is no sunshine, and you get wet and lose body heat easily
- When the weather turns and rain and wind come together, there is a risk of hypothermia even in summer
Use the calculated temperature as a preparation guide meaning “it may get this cold”, and let it help you decide to carry one more layer. In the hiking water and trail food calculator, enter the trailhead elevation and temperature and the summit elevation and wind speed, and it shows the summit temperature, the feels-like temperature and what to wear. How to estimate the course time used in the calculations is explained in the course time article.
FAQ
- How much does the temperature drop for every 1,000 m of elevation?
- About 6°C. It drops about 0.6°C for every 100 m, so for 1,000 m it is 0.6 × 10 = 6°C. If the foot of the mountain is 20°C, a summit 1,000 m higher will be about 14°C.
- How do I calculate the temperature at the summit of Mount Fuji?
- Subtract 0.6 × 3,776 ÷ 100 = about 22.7°C from the seaside (0 m) temperature. If the seaside is 30°C, the summit is about 7°C; if it is 20°C, about −3°C. Check the actual summit temperature in a mountain weather forecast as well.
- How do I work out the feels-like temperature?
- In hiking, a common rule of thumb is that each 1 m/s of wind lowers the feels-like temperature by about 1°C. If the summit is 14°C with a 5 m/s wind, it feels like about 9°C. If you are wet with sweat, it feels even colder.
- Do I need a jacket even on a low mountain?
- Yes. A 500 m climb means about 3°C colder, and wind at the summit makes it feel colder still. Your body cools quickly during breaks, so carry a light jacket or rain jacket.
- Is the temperature in the weather forecast the summit temperature?
- The temperature in an ordinary forecast is the value at an observation point in that area, usually on flat land. Calculate the summit temperature from the elevation difference to the observation point, or check a mountain weather forecast service.
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