The Oceans Of The World By Size

Earth is arguably a misnomer. About 71 percent of the planet's surface hides beneath saltwater, and roughly 96.5 percent of all the water on Earth sits in the ocean, which makes "Ocean" a far more honest name for the place. Technically there is just one global ocean, a single body of water uninterrupted by land, but for the sake of maps and sanity it gets sliced into five basins: the Pacific, the Atlantic, the Indian, the Southern, and the Arctic. Each takes its name from the part of the world it washes against.

Those dividing lines are not fixed in stone, or rather, not fixed in water. The boundaries between the oceans have shifted over the centuries for reasons both scientific and political, and they may well shift again. For now, here are the five oceans ranked by size, largest first, with every measurement given in both metric and imperial so you can picture the scale either way.

1. The Pacific Ocean

At 168,723,000 square kilometers (about 65,144,000 square miles), the Pacific is the undisputed heavyweight of the planet's oceans, covering roughly 46.6 percent of the global ocean. That is nearly half of all the seawater on Earth held in a single basin. It spans the planet's full north-to-south reach, sitting between the Arctic and the Antarctic and filling most of the gap between Asia and the Americas, with a coastline that unspools for 135,663 kilometers (about 84,300 miles). The countries on its rim read like a world tour: Russia, China, Canada, the United States, Mexico, Peru, and Chile. Scattered across it are roughly 25,000 islands, and it laps the shores of an entire island continent, Australia.

The Pacific is not just the widest ocean, it is also the deepest on average, running 3,970 meters (about 13,025 feet) from top to bottom. It also hides the lowest spot on the planet, the Mariana Trench, whose Challenger Deep bottoms out at about 10,994 meters (36,070 feet) below the waves. Drop Mount Everest into that chasm and the mountain's 8,849-meter (29,032-foot) summit would still sit more than a mile underwater. With trenches like that, it is no surprise the Pacific holds 50.1 percent of all the water in the global ocean. All that room leaves space for a wildly varied cast of residents, including orcas, dugongs, giant squid, and sea slugs barely bigger than a fingernail.

This enormous ocean has set the stage for some of history's biggest moments. Most famously, it became the principal theater of the Pacific War during World War II, the saltwater arena for pivotal clashes like the Battles of Midway and Iwo Jima.

2. The Atlantic Ocean

The Atlantic covers roughly 85,133,000 square kilometers (about 32,870,000 square miles), which sounds enormous until you remember the Pacific is nearly twice its size. Even so, it runs along 111,866 kilometers (about 69,500 miles) of coastline. Its western shore presses against the Americas, brushing countries like Brazil and Argentina, while its eastern shore meets Europe and a long line of African nations. Like the Pacific, it reaches deep into both hemispheres, though it is far narrower, and on a world map its unmistakable S-shape gives it away at a glance.

On average it runs 3,646 meters (about 11,962 feet) deep, but its floor drops far lower at the Milwaukee Deep, the Atlantic's deepest point, which sinks to 8,380 meters (27,493 feet) inside the Puerto Rico Trench. That cold, crushing pocket went unvisited until December 2018, when Victor Vescovo, a former naval officer turned deep-sea explorer, became the first person ever to reach the bottom of the Atlantic.

The ocean owes its name to Greek mythology and to Atlas, the Titan condemned to hold up the sky for all eternity. It is a fitting label, because the Atlantic has seen its share of weight and tragedy, including the sinking of the Titanic in 1912 and the torpedoing of the RMS Lusitania in 1915.

3. The Indian Ocean

At 70,560,000 square kilometers (about 27,243,000 square miles), the Indian Ocean takes the bronze medal, making up roughly 19.5 percent of the global ocean and lining 66,526 kilometers (about 41,300 miles) of coast. Unlike the first two, it does not run pole to pole. Instead it sits in a giant pocket, walled off to the north and cradled by East Africa, southern Asia, and western Australia. It also claims Madagascar, the fourth-largest island on Earth.

Do not let the smaller footprint fool you. The Indian Ocean averages roughly 100 meters (about 330 feet) deeper than the Atlantic, at 3,741 meters (about 12,274 feet). It has relatively few deep trenches, but it does hold the long Java Trench, also known as the Sunda Trench, where the ocean reaches its lowest point at about 7,190 meters (roughly 23,600 feet) down.

The Indian Ocean is the only one named for a country, and that name is far older than most people guess. The Roman scholar Pliny the Elder was already calling it Oceanus Indicus, after the Indus River, almost 2,000 years ago, and the modern form was firmly on Latin maps by 1515. For centuries it also went by the plainer "Eastern Ocean," the counterpart to the Atlantic's old "Western Ocean." The India-centric name has drawn the occasional objection over the years, including from Pakistan, but it has stuck all the same.

4. The Southern Ocean

The Southern Ocean measures roughly 21,960,000 square kilometers (about 8,479,000 square miles), or 6.1 percent of the global ocean, which makes it dramatically smaller than the big three above it. The Pacific alone is about seven times its size. There is also a fair bit of arguing over where it actually begins, since it has no continents to fence it in. The United States draws the line at the 60^th parallel south, a ring of latitude far below the equator, and everything beyond that belt counts as the Southern Ocean as it wraps the whole way around Antarctica.

Small does not mean shallow. The Southern Ocean averages 3,270 meters (about 10,728 feet) deep, only around 700 meters (about 2,300 feet) less than the mighty Pacific. Its surroundings look barren and frozen, yet the water teems with life: whales, seals, and vast rafts of penguins. Many of those animals now face mounting pressure from pollution and the steady squeeze of climate change.

For most of history, mapmakers counted only four oceans. The Southern was formally proposed to the International Hydrographic Organization in 2000, and not every member has signed off, so its status is not yet unanimous. Even so, plenty of countries, the United States among them, treat it as the legitimate fifth ocean.

5. The Arctic Ocean

The Arctic is the runt of the litter, the smallest of the five oceans at 15,558,000 square kilometers (about 6,007,000 square miles), a mere 4.3 percent of the global ocean. It punches above its weight on coastline, though, with 27,421 kilometers (about 17,000 miles) more shoreline than the Southern Ocean. Sitting at the top of the world, it laps the northern coasts of five nations: Canada, the United States, Russia, Norway, and Denmark by way of Greenland. Iceland sits just off its southern edge, straddling the line between the Arctic and the Atlantic, and the ocean is studded with islands such as the Queen Elizabeth Islands and the Russian Arctic islands.

The Arctic Ocean is also the shallowest of the bunch by a wide margin, averaging just 1,205 meters (about 3,953 feet), barely a third of the Pacific's average depth. It is the coldest ocean too, yet it is warming two to three times faster than the planet as a whole, which is steadily reshaping the ice, the wildlife, and the communities that depend on it.

Its name has nothing to do with the polar bears that prowl its ice. It comes from the Greek word arktos, meaning "bear," a nod to the constellations Ursa Major and Ursa Minor, the Great Bear and the Little Bear, that wheel overhead in the northern sky. Some oceanographers still prefer to call it the Arctic Sea, but the International Hydrographic Organization officially recognizes it as an ocean.

The Five Oceans At A Glance

Here is how the five basins stack up by area, volume, average depth, and coastline, with each figure shown in metric and then imperial.

One World Ocean, Five Names

For all the borders drawn on maps, the truth is that there is really just one ocean. Water flows freely between the five basins, carrying heat, salt, nutrients, and the occasional wandering whale around the entire planet in one connected system. Splitting that system into a Pacific, an Atlantic, an Indian, a Southern, and an Arctic helps with measuring, naming, and studying it, but every drop belongs to the same global sea. Whether you count four oceans or five, the water does not much care. It just keeps moving.