Cloud Base Calculator
Estimate cloud height with clear AGL and MSL results.
Estimates the base of convective clouds from surface temperature and dew point. This is not an observed ceiling or a prediction of every cloud layer.
Formula, units & limitations
AGL (ft) ≈ 400 × (temperature °C − dew point °C). MSL (ft) = AGL + station elevation. Both temperatures convert to Celsius before calculating, so unit changes preserve the result. This uses a rounded 2.5 °C per 1,000 ft spread rule.
Supported inputs: altitude −2,000 to 30,000 ft (direct PA −5,000 to 30,000 ft); QNH 25–35 inHg; temperature and dew point −100 to 60 °C. These ranges bound this calculator, not aircraft operating limits.
For current airport weather, open official METAR observations. Weather values are entered manually.