By far the largest of the four oceans, the Pacific Ocean covers nearly one-third of the globe, or an area of approximately 64 million square miles. The land area of the United States, including Alaska and Hawaii, covers less than 4 million square miles. The Pacific Ocean is immense. All the continents could be placed into it and there would still be room left over. Even with the many topographic features found on the seafloor, such as plateaus, ridges, trenches, and seamounts, it has an average depth of 13,000 feet. The Pacific Ocean is approximately 11,000 miles wide at the equator.

Not only is the Pacific Ocean the largest and deepest, it is probably the most violent of all oceans. The Pacific Ocean has typhoons in the equatorial regions, nearly 300 active volcanoes which vent steam and smoke on its borders, and tidal waves that are periodically unleashed.

Unlike the basin floors of the Atlantic and Indian Oceans, the Pacific Ocean is characterized by the Central Pacific Trough. This feature extends from the Aleutian Islands southward to Antarctica and from Japan to the west coast of North America. The basin floors are not completely flat, and ridges and seamounts abound. Along with a number of deep ocean trenches, the Pacific Ocean has many flat-topped seamounts, or guyots. These are rarely found in other oceans.