The Indian Ocean is often thought of incorrectly as a tropical ocean. The Indian Ocean stretches southward to Antarctica. It is triangular and bordered by Africa, Asia, Antarctica, and Australia. Although it covers about 28.5 million square miles, it is smaller than the Atlantic Ocean and less than half the size of the Pacific Ocean. The maximum width is 6,200 miles between the southernmost portions of Africa and Australia. The Indian Ocean contains about 20 percent of the earth's water surface. Many island nations are found within the boundaries of this ocean: Madagascar, which is the world's fourth largest island, the Seychelles, the Maldives, Mauritius, and Sri Lanka.

The average depth of the Indian Ocean is about 12,750 feet. The deepest is 24,440 feet in the Java Trench in the extreme northeast corner of the basin. The Indian Ocean, like the Atlantic Ocean, is divided by a mid-ocean ridge, the Mid-Indian Ocean Ridge, which separates the basin into nearly equal portions. The ocean's continental shelves are narrow, averaging 125 miles in width except off Australia's western coast where it broadens to 600 miles.