Cloud base height calculator
Enter the surface temperature and dew point to estimate where clouds begin to form, a common method for pilots and weather watchers.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter surface air temperature, surface dew point and temperature unit.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Height (m) ≈ 125 × (T − Td) in °C, and feet = metres ÷ 0.3048. An approximation of the lifting condensation level.
Example
Inputs: Surface air temperature = 30, Surface dew point = 18, Temperature unit = Celsius (°C). Result: Cloud base above ground: 1,500 m; In feet: 4,921 ft; Temperature and dew point spread: 12 °C.
Limits and caveats
- A rough estimate for convective cumulus; it does not suit layered or frontal cloud.
- The height is above the measuring site, not above sea level.
Questions about this tool
Why does cloud height depend on the dew point?
Rising air cools faster than its dew point falls, and they meet about 125 m up for each degree of spread.
Can I use this for flying?
It gives a quick idea only; official airport weather reports are the reference.
What does a zero spread mean?
The air is saturated at the surface, so fog or very low cloud is likely.