The Indian Ocean is the third largest of the world's oceanic divisions, covering about 20% of the water on the Earth's surface. It is bounded on the north by Asia (including the Indian subcontinent, after which it is named); on the west by Africa; on the east by Indochina, the Sunda Islands, and Australia; and on the south by the Southern Ocean (or, traditionally, by Antarctica). One component of the all-encompassing World Ocean, the Indian Ocean is delineated from the Atlantic Ocean by the 20° east meridian running south from Cape Agulhas, and from the Pacific by the 147° east meridian. The northernmost extent of the Indian Ocean is approximately 30° north in the Persian Gulf. The Indian Ocean has asymmetric ocean circulation. This ocean is nearly 10,000 kilometres (6,200 mi) wide at the southern tips of Africa and Australia; its area is 73,556,000 square kilometres (28,400,000 mi²), including the Red Sea and the Persian Gulf.
The ocean's volume is estimated to be 292,131,000 cubic kilometers (70,086,000 mi³). Small islands dot the continental rims. Island nations within the ocean are Madagascar, the world's fourth largest island; Comoros; Seychelles; Maldives; Mauritius; and Sri Lanka. The archipelago of Indonesia borders the ocean on the east. The ocean's importance as a transit route between Asia and Africa has made it a scene of conflict. Because of its size, however, no nation successfully dominated most of it until the early 1800s when the United Kingdom controlled much of the surrounding land.