How cloud base height is estimated
Cumulus cloud bases form at the lifted condensation level (LCL), the altitude at which rising, cooling air reaches saturation and water vapor condenses into visible cloud droplets.
The formula
This calculator uses a widely used meteorological approximation known as Espy’s equation: Height (m) ≈ 122 × (Temperature − Dew Point), with both temperatures in °C. The relationship holds because temperature drops roughly 1°C per 100 m of ascent (dry adiabatic lapse rate) while dew point drops more slowly, so the gap between them narrows to zero at the condensation level.
This is an approximation for fair-weather cumulus clouds under typical atmospheric conditions; it doesn’t account for unusual lapse rates, frontal boundaries, or non-cumulus cloud types. This calculator is for general educational and planning purposes.