Which type of cloud is lowest in the sky?

Thus, the 10 types are:

Low-level clouds (cumulus, stratus, stratocumulus) that lie below 6,500 feet (1,981 m)

Middle clouds (altocumulus, nimbostratus, altostratus) that form between 6,500 and 20,000 feet (1981–6,096 m)

High-level clouds (cirrus, cirrocumulus, cirrostratus) that form above 20,000 feet (6,096 m)