The Sahara is the largest subtropical hot desert and third largest desert after Antarctica and the Arctic. At over 9,400,000 square kilometres , it covers most of North Africa, making it almost as large as China or the United States. The Sahara stretches from the Red Sea to the east, including parts of the Mediterranean coasts to the Atlantic Ocean to the west. To the south, it is delimited by the Sahel, a belt of semi-arid tropical savanna that composes the northern region of central and western Sub-Saharan Africa.