Cloud Base Calculator
Estimate the height of cumulus cloud bases.
The temperature–dew point spread predicts how high cumulus clouds form.
How the Math Works
The Cloud Base Calculator uses a simple yet powerful formula to estimate cloud height: height ≈ 125·(T − T_dew) metres. Here, T represents the air temperature at ground level (in degrees Celsius), and T_dew is the dew point temperature (also in Celsius). The difference between these two values, known as the 'dew point depression,' indicates how much the air needs to cool to reach saturation. The constant 125 is derived from the average rate at which temperature decreases with altitude in unsaturated air (approximately 0.65°C per 100 metres). By multiplying the dew point depression by 125, we convert the temperature difference into an estimated height above ground where condensation begins and clouds form.
Practical Applications
To use this calculator practically, first measure or obtain the current air temperature and dew point at your location. These values can be found using a weather station, weather app, or by checking online weather services. Simply subtract the dew point from the air temperature, then multiply the result by 125 to get the cloud base height in metres. For example, if the air temperature is 20°C and the dew point is 10°C, the calculation would be: height ≈ 125·(20 − 10) = 1250 metres. This tells you that cumulus clouds are likely forming at approximately 1,250 metres above ground level.
Day-to-Day Use
Knowing your cloud base height has practical benefits in everyday life. If you're planning outdoor activities like hiking, flying drones, or photography, understanding cloud altitude helps you predict if conditions are right for cloud formation or if they might interfere with your plans. Pilots and glider enthusiasts use this information to assess flight conditions and find lift. Gardeners and farmers can estimate when dew or low clouds might form, affecting morning frost risk or plant moisture. Additionally, this knowledge helps you appreciate weather patterns visually — when you see clouds forming at the predicted height, you can connect the science to what you observe in the sky.
Worked example
25 °C with 15 °C dew point → about 1250 m (4100 ft).
FAQ
Why does a small spread mean low clouds?
The air needs less lifting to cool to saturation.