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Low clouds are found from between ground level and 6,500 feet (2,000 meters) and include (from highest to lowest) stratocumulus, stratus, cumulus, and cumulonimbus. Stratocumulus clouds are large and lumpy, round or rolled-looking, and often cover the entire sky. Stratus clouds are generally dark and appear as streaks across the sky or as a grey layer hanging above the Earth. Stratus clouds are generally shapeless.
Cumulus clouds range in size from the small puffball-like forms to huge dome-topped thick piles of "woolpack" that often develop into thunderclouds. These storm clouds, cumulonimbus, may range in thickness from about 1 to 3 miles (1.6 to 4.8 kilometers) in Great Britain to 8 or 9 miles (12.9 or 14.5 kilometers) near the equator.