What is the world's largest desert?

Most experts agree that a desert is an area of land that receives 10 inches (25.4 centimeters) or less of precipitation per year. The world's deserts can be categorized into five kinds, according to the causes of their dryness: subtropical, coastal, rain shadow, interior, and polar. 

The subtropical Sahara is the largest hot desert at 3.5 million square miles (9 million square kilometers), but Antarctica, a polar desert covering 5 million square miles (13 million square kilometers), is the largest desert overall.
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