Different types of clouds vary in distance from Earth's surface, but range from quite near the ground to as high as 50,000 feet. Heights of the three main types of clouds also vary depending on latitude.
The three main types of clouds are stratus clouds below 6,500 feet, "alto-" clouds such as altostratus and altocumulus between 6,500 and 20,000 feet and cirrus clouds 20,000 feet and above. Thunderstorm clouds can reach as high as 50,000 feet, or more than nine miles high.
Clouds form when invisible humidity in the air cools and condenses on dust or salt particles and turns into ice crystals or water droplets and becomes visible.