Although they look light and fluffy floating in the sky, clouds actually consist of water droplets and are heavy. A one cubic kilometer (1 km³ meaning 1 km X 1 km X 1 km or 0.6 miles X 0.6 miles X 0.6 miles) cumulus cloud has an estimated weight of 2.211 billion pounds (1.003 billion kilograms). Clouds float because they are suspended on dry air. An equal volume (1 km³) of dry air weighs 2.220 billion pounds (1.007 billion kilograms). Dry air has a density of 1.007 kilograms/cubic meter while the density of the moist cloud is 1.003 kilograms/cubic meter. Clouds float because they are less dense than the drier air.