All empires at their greatest extent
British Empire - 33.7 million km2 (1922)[2]
Mongol Empire - 33.0 million km2 (1270 or 1309)[3][4]
Russian Empire - 23.7 million km2 (1866)[3][4]
Spanish Empire - 20.0 million km2 (ca. 1740-1790)[5]
Qing Empire, China - 14.7 million km2 (1790)[3][4]
Yuan Dynasty - 14.0 million km2 (1310)[4]
Umayyad Caliphate - 13.0 million km2 (720 or 750)[6]
Second French Colonial Empire - 12.3 million km2 (1938)[5]
Abbasid Caliphate - 11.1 million km2 (750)[4]
Portuguese Empire - 10.4 million km2 (1815)[5]
American Empire - 9.8 million km2 (1899)[4]
Rashidun Caliphate - 9.0 million km2 (654)[4][7]
Empire of Brazil - 8.5 million km2 (1880)[5]
Achaemenid Empire, Persia - 8.0 million km2 (480 BC)[8]
Japanese Empire - 7.4 million km2 (1942)[5]
Han Empire, China - 6.5 million km2 (100)[9]
Roman Empire - 6.5 million km2 (117)[10]
Ming Empire, China - 6.5 million km2 (1450)[3][4]
Göktürk Khaganate - 6.0 million km2 (557)[3][9]
Golden Horde Khanate - 6.0 million km2 (1310)[3][4]
Uyghur Khaganate - 5.5 million km2 (800)[3][4]
Tang Empire, China - 5.4 million km2 (715)[3][4]
Macedonian Empire - 5.2 million km2 (323 BC)[3][11]
Ottoman Empire - 5.2 million km2 (1683, 1829 or 1850)[3][4]
Fatimid Caliphate - 5.1 million km2 (969)[3][4]
Maurya Empire, India - 5.0 million km2 (250 BC)[3]
Northern Yuan Dynasty (Oirats), Mongolia - 5.0 million km2 (1550)[4]
Xin Dynasty, China - 4.7 million km2 (10)[9]
Tufan (Tibet) Empire - 4.6 million km2 (800)[3][4]
Pala Empire, India - 4.6 million km2 (850)
Timurid Empire - 4.6 million km2 (1405)[3][4]
Mughal Empire, India - 4.6 million km2 (1690)[3][4]
First Mexican Empire - 4.4 million km2 (1822)[citation needed]
Xiongnu Empire - 4.03 million km2 (176 BC)[12]
Hunnic Empire - 4.0 million km2 (441)[9]
Hepthalite Khanate (White Huns), India - 4.0 million km2 (490)[9]
Eastern Turks Khanate - 4.0 million km2 (624)[9]
Afsharid Dynasty, Persia - 4.0 million km2 (1747)[citation needed]
Western Turks Khanate- 4.0 million km2 (630)[9]
Rouran Khaganate (Juan-juan) - 4.0 million km2 (AD 405)[3][9]
Seleucid Empire - 3.9 million km2 (301 BC)[3][11]
Great Seljuq Empire - 3.9 million km2 (1080)[3][4]
Italian Empire - 3.8 million km2 (1940)[citation needed]
Kushan Empire, India- 3.8 million km2 (200)[9]
Ilkhanate - 3.75 million km2 (1310)[3][4]
Dutch Empire - 3.7 million km2(1940)[citation needed]
Chola Dynasty, India - 3.6 million km2 (1050)[citation needed]
Khwarazmian Empire - 3.6 million km2 (1218)[4]
Nazi Germany - 3.6 million km2 (1942)[citation needed]
Sassanid Empire, Persia - 3.5 million km2 (620)[3]
Gupta Empire, India - 3.5 million km2 (400)[3]
Chagatai Khanate - 3.5 million km2 (1310 or 1350)[3][4]
Safavid Dynasty, Persia - 3.5 million km2 (1512)[citation needed]
German Empire - 3.5 million km2 (1914)[citation needed]
http://en.wikipedia.org/wiki/List_of_largest_empireshttp://en.wikipedia.org/wiki/Mongol_Empire