Calculating cloud height is the perfectionist's alternative to guessing how high clouds are. Clouds form as air masses rise -- generally with heat -- and expand. This expanded air mass is cooler and has lower pressure, resulting in less ability to hold moisture. When the moisture in the air is greater than it can hold, water vapour in the air condenses, causing clouds. Dew point is the temperature at which air can no longer hold its moisture. By knowing both the dew point and temperature, it's possible to calculate the base of cumulus clouds.
Find the current outdoor temperature in degrees Fahrenheit.
Find the current dewpoint in degrees Fahrenheit
Plug those two numbers into the following formula:
Cloud Base (ft) = 250 * (Outdoor Temperature (ºF) - Dewpoint (ºF))
If you don't like math or only have the temperature in degrees Celsius, use an online calculator to do the work for you (see Resources). It accepts both Fahrenheit and Celsius measurements.