The largest desert in the world is the Antarctic Desert, which covers about 14.2 million square kilometers (roughly 5.5 million square miles). Deserts are defined by very low precipitation, not heat, so the cold, dry polar regions count. The Arctic Desert is second at about 13.9 million square kilometers.
The Sahara in North Africa is the largest hot desert, at about 9.2 million square kilometers, and the third-largest desert overall.