About this tool
Cloud Base / Ceiling Calculator is a free, in-browser tool that estimates the height of the cumulus cloud base — the lifted condensation level — from the surface temperature and dew point. Enter both temperatures in °C or °F, and optionally the field elevation, and the estimated base is shown in feet above ground, metres, and feet above sea level, all computed on your device.
It uses the standard dew-point-spread rule. In Celsius the base above ground is ((T − Td) ÷ 2.5) × 1000 feet, because rising air cools at roughly 2.5 °C per 1,000 feet until it reaches the dew point; in Fahrenheit the divisor is 4.4 °F per 1,000 feet. Adding the field elevation gives the base in feet MSL. When the temperature and dew point are equal the air is already saturated, so the tool reports a base at the surface.
This gives a quick idea of the fair-weather cumulus ceiling for VFR planning, but it applies to convective cloud on a well-mixed day and is only an estimate — not for real-world navigation. Always check actual ceilings against METARs, TAFs and other official sources before flight.
Frequently asked questions
How is the cloud base estimated?
From the temperature–dew point spread. In Celsius the base above ground ≈ ((T − Td) ÷ 2.5) × 1,000 feet; in Fahrenheit ≈ ((T − Td) ÷ 4.4) × 1,000 feet. Adding field elevation converts the height above ground to a height above sea level.
Why does a bigger spread mean higher cloud?
Air lifted from the surface cools until it reaches its dew point and condenses. A larger gap between temperature and dew point means the parcel must rise further to cool that much, so cloud forms higher up. A small spread produces a low base.
What kind of cloud does this apply to?
Convective, fair-weather cumulus forming by surface heating and lifting on a well-mixed day. It does not predict stratus, frontal cloud or ceilings driven by other processes, so use it only as a rough guide to the cumulus base.
Is this a substitute for an official ceiling report?
No. It is an estimate, not for real-world navigation. Actual ceilings depend on the full atmospheric profile — always use current METARs, TAFs, area forecasts and other official sources for flight decisions.
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