How do I estimate cloud base height?

The simplest method is the temp-dew point spread: multiply the difference between air temperature and dew point by 125 to get the cloud base height in metres above ground level. For example, if the temperature is 15°C and dew point is 10°C, the cloud base is approximately 625m above you.

Why is cloud base important for hiking?

Walking in cloud means zero visibility, requiring compass navigation skills. Knowing the cloud base helps you decide whether to attempt a summit or choose a lower-level route. In UK mountains, cloud base is frequently below summit height — checking beforehand prevents dangerous situations.

Where can I find dew point data?

The Met Office MWIS (Mountain Weather Information Service) reports dew point and cloud base forecasts for UK mountain areas. Airport weather reports (METARs) include dew point. You can also estimate dew point from the condensation on a cold water bottle or using a sling psychrometer.

How accurate is this calculation?

The temp-dew spread method gives a reasonable estimate for convective clouds (cumulus). It is less accurate for frontal cloud systems, temperature inversions, or when conditions are changing rapidly. Always cross-check with the MWIS forecast and observe conditions as you ascend.

CampCalcs

Cloud Base Calculator

Estimate cloud base height from temperature and dew point readings.

Air Temperature

Dew Point

Your Altitude

Altitude where you measure temp

How We Calculate This

Cloud Base Formula

Cloud base (m AGL) = (Temperature - Dew point) x 125

Cloud base (m ASL) = Cloud base AGL + Station altitude

The temperature decreases at ~1°C per 125m of altitude while the dew point decreases slower. Where they meet, clouds form.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify conditions and use proper safety equipment outdoors.