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The total mass of the hydrosphere is about 1.4 quintillion metric tons ( long tons or short tons), which is about 0.023% of Earth's total mass. Less than 3% is freshwater; the rest is saltwater, almost all of which is in the ocean. The area of the World Ocean is about 361.9 million square kilometers (139.7 million square miles), which covers about 70.9% of Earth's surface, and its volume is approximately 1.335 billion cubic kilometers (320.3 million cubic miles). This can be thought of as a cube of water with an edge length of . Its average depth is about , and its maximum depth is at the Mariana Trench. Nearly half of the world's marine waters are over deep. The vast expanses of deep ocean (anything below ) cover about 66% of Earth's surface. This does not include seas not connected to the World Ocean, such as the Caspian Sea.
361.9 million square kilometers