Cloud Base Calculator
Estimate the base of convective (cumulus) cloud from the temperature and dew point — or pull the current values straight from an airport's METAR.
Autofill temperature & dewpoint from the current METAR.
Temperature
Dewpoint
Estimated cloud base (AGL)
4,800 ft
Approx. base (MSL)
4,800 ft
Spread is 12°C. This estimates convective (cumulus) bases only — layered/stratus cloud, fronts and terrain aren't captured. Verify against the METAR/TAF and what you see.
How this works
As air is lifted it cools at the dry-adiabatic rate (~3°C/1,000 ft) while its dew point falls much more slowly, so temperature and dew point converge with height. Cloud forms where they meet — the lifting condensation level.
The rule of thumb: cloud base (AGL) ≈ 400 ft × (temperature − dew point) in °C.
This applies to convective cloud on a well-mixed day. Stratus, frontal cloud and orographic lift form by other mechanisms and aren't captured — always cross-check the METAR/TAF and what you actually see.
For reference and training only. Not for navigation or flight planning — always verify against official current sources.