How large was Genghis Khan's empire?

The Mongol Empire, established by Genghis Khan, covered between 11 to 12 million square miles at its peak. It extended from Eastern Europe to the Sea of Japan, north into Siberia and south into the Iranian Plateau. It was the largest land empire in history.

The Mongol Empire existed from approximately 1206 to 1368, originating in Central Asia. It was created through the unification of nomadic tribes in Mongolia, under leader Genghis Khan. He extended his empire by invading the Qara Khitai, Caucasus, Khwarezmid Empire, Western Xia and Jin dynasties. At the time of his death in 1227, the Empire covered most of Central Asia and China and his successors continued his legacy.