What Is the Biggest Ocean?

Short answer

• The biggest ocean is the Pacific Ocean. It is the largest by surface area, the largest by volume of water, and the deepest on average, and it also contains the deepest known point in the oceans, Challenger Deep in the Mariana Trench. On the consistent set of figures used in this article, the Pacific covers 168,723,000 square kilometers, holds 669,880,000 cubic kilometers of water, has an average depth of 3,970 meters, and reaches about 10,935 meters at Challenger Deep. No other ocean comes close on any of those measures, which is why the answer does not change when you change the measure.

A Simple Question With a Measurement Problem

Asking for the biggest ocean sounds like asking for one fact. In practice, “biggest” can mean several different things, and a careful answer has to say which meaning it is using. An ocean could be biggest in the sense of covering the most surface, holding the most water, being deepest on average, or containing the single deepest point. For most comparisons in everyday life, those meanings could point in different directions. A wide, shallow lake can cover more ground than a narrow, deep one while holding less water. A long, thin sea can have a huge coastline without having a huge area.

The Pacific Ocean is unusual because it wins on every one of those measures at once. This article compares all five named oceans on the same basis, explains how each measure is worked out, shows why the figures sometimes differ between sources, and explains why the area ranking and the volume ranking agree here even though they do not have to.

This is also a different question from asking how many oceans there are. Counting the oceans is about naming and dividing one continuous world ocean into parts. Ranking them by size is about measuring those parts once the divisions are agreed. The divisions used here are the five commonly named oceans: the Pacific, Atlantic, Indian, Southern, and Arctic oceans. The boundaries between them are conventions, not fences in the water, so moving a boundary moves area and volume from one named ocean to another without changing the total.

The Answer in Full: The Pacific Ocean

The Pacific Ocean stretches from the Arctic region in the north to the Southern Ocean in the south, and it is bounded by Asia and Australia in the west and by the Americas in the east. It is the ocean that dominates any map of Earth, and it dominates the numbers just as clearly.

On the dataset used for the comparison table in this article, the Pacific covers 168,723,000 square kilometers (65,144,000 square miles). That is about 46.6 percent of the total area of the world ocean, which is 361,934,000 square kilometers. Put another way, nearly half of all the ocean surface on Earth belongs to a single named ocean. The same dataset gives the Pacific a volume of 669,880,000 cubic kilometers (160,713,000 cubic miles), which is about 50.2 percent of the world ocean volume of 1,335,000,000 cubic kilometers. The Pacific therefore holds just over half of all ocean water.

Its average depth on that dataset is 3,970 meters (13,025 feet). Average depth is not a guess and it is not the depth you would find at a random spot. It is the volume divided by the area, so it describes the basin as a whole. A higher average depth means that, square kilometer for square kilometer, the basin holds more water. The Pacific has both the largest area and, on this dataset, the greatest average depth of the five oceans, so its volume lead is even larger than its area lead. That combination is the key to the whole ranking.

The Pacific is also where the ocean reaches its greatest depth. Challenger Deep, at the southern end of the Mariana Trench in the western Pacific, is the deepest known point in the oceans. A 2021 study based on submersible dives in June 2020, published with authors from the National Oceanic and Atmospheric Administration (NOAA), gives its deepest observed seafloor depth as 10,935 meters below mean sea level, with an uncertainty of 6 meters at the 95 percent confidence level. Older and rounded figures of about 11,000 meters, or about 36,000 feet, describe the same place with less precision. The difference between those figures is a matter of measurement method, exact location within the trench, and rounding, not a disagreement about which ocean holds the deepest point.

For scale, the highest point on land given in the same Britannica discussion of ocean depth is Mount Everest at 8,850 meters. If Everest stood on the floor of Challenger Deep at 10,935 meters, its summit would still sit about 2,085 meters below the surface. That comparison is often quoted because it turns an abstract depth into something a reader can picture, but it also makes a real point: the vertical range of the oceans, from sea level down to Challenger Deep, is greater than the vertical range of the land, from sea level up to Everest.

All Five Oceans Compared on the Same Basis

The table below uses one consistent dataset so that the oceans can be compared fairly. The figures come from Encyclopaedia Britannica, which reproduces a table whose data source is Eakins and Sharman, Volumes of the World’s Oceans from ETOPO1, NOAA National Geophysical Data Center, Boulder, Colorado, 2010. Using one dataset matters. Mixing an area figure from one source with a volume figure from another can produce an average depth that no source actually supports, and mixing boundary definitions can make an ocean look larger or smaller for no physical reason.

Ocean	Area (square kilometers)	Volume (cubic kilometers)	Average depth (meters)
Pacific Ocean	168,723,000	669,880,000	3,970
Atlantic Ocean	85,133,000	310,411,000	3,646
Indian Ocean	70,560,000	264,000,000	3,741
Southern Ocean	21,960,000	71,800,000	3,270
Arctic Ocean	15,558,000	18,750,000	1,205
World ocean (total)	361,934,000	1,335,000,000	3,688

Read the table in three passes, one for each measure. By area, the order is Pacific first, then Atlantic, then Indian, then Southern, then Arctic. By volume, the order is exactly the same. By average depth, the Pacific is again first, followed by the Indian Ocean, then the Atlantic, then the Southern Ocean, and finally the Arctic, which is by far the shallowest. The Atlantic and Indian oceans swap second and third place between the area ranking and the average depth ranking, which is a useful reminder that area and depth are separate facts. The Pacific does not swap. It leads on all three.

Three comparisons give the Pacific lead its proper scale. First, the Pacific at 168,723,000 square kilometers is almost twice the Atlantic at 85,133,000 square kilometers. Second, the Pacific is larger than the Atlantic and Indian oceans combined, since those two together total 155,693,000 square kilometers, which is still about 13,030,000 square kilometers less than the Pacific alone. Third, the Pacific is more than ten times the area of the Arctic Ocean, the smallest ocean, at 15,558,000 square kilometers. The volume gap is even wider at the small end: the Pacific holds about 35 times as much water as the Arctic Ocean.

The Arctic Ocean is extreme in the opposite direction. It is the smallest ocean by area and by volume, and its average depth of 1,205 meters is less than one third of the Pacific average, reflecting a basin with extensive shallow shelf seas. “Smallest” here describes the basin as measured, not a judgment about importance.

How Ocean Size Is Measured

Understanding the table means understanding four measures and what each one leaves out.

Surface area is the area of the ocean surface within the agreed boundaries of that ocean, measured from maps and satellite based bathymetry, which is the measurement of seafloor depth. It depends on where the boundary is drawn. In the dataset used here, the Southern Ocean includes all marine waters south of 60 degrees south latitude. Other definitions draw the boundary elsewhere, for example at the Antarctic Convergence, where cold Antarctic waters meet warmer waters to the north. Move that line and area shifts between the Southern Ocean and its neighbors. That is why different reputable sources give different Pacific area figures, for example about 165,250,000 square kilometers when the Pacific is defined with a southern Antarctic border. The ranking does not change, because the shift is far too small to close a gap of more than 80,000,000 square kilometers between the Pacific and the Atlantic.

Volume is the amount of water in the basin, worked out by dividing the basin into small cells, multiplying the area of each cell by its depth, and adding the results. It is the best single measure of “how much ocean” there is, because it counts water rather than surface. It is also the hardest to measure directly, since it depends on knowing the depth everywhere, including remote places where direct soundings are sparse. Satellite gravity data help fill those gaps, but the result remains an estimate, which is why volumes are usually quoted to the nearest million cubic kilometers.

Average depth, also called mean depth, is volume divided by area. It is a derived figure, not a depth measured at any one place. Its value is that it lets you compare basins fairly: two oceans with the same area can hold very different amounts of water if one basin is on average much deeper. It also explains why the Pacific volume lead is larger than its area lead. The Pacific is not only wider, it is on average deeper than the Atlantic, so each square kilometer of Pacific surface corresponds to more water than each square kilometer of Atlantic surface.

Greatest depth, or maximum depth, is a different kind of fact. It is the depth of the single deepest surveyed point in the ocean, not a typical depth. A single trench can make an ocean the holder of the deepest point without making its average depth the greatest, although in the Pacific both are true. Greatest depth is also the figure most sensitive to new surveys, because a new measurement in one small basin can revise it by tens of meters while leaving the area and volume figures almost untouched. That is exactly what has happened at Challenger Deep, where successive surveys have reported depths around 10,900 meters to just over 11,000 meters depending on the basin surveyed, the instrument used, and the corrections applied for water properties, air pressure, and gravity.

Coastline length should be treated with caution as a measure of size. The measured length grows as the measuring scale gets finer, because smaller bays and inlets are counted, so coastline figures for the same ocean can differ wildly between sources. This article therefore does not rank the oceans by coastline. A long coastline can reflect a complicated shore rather than a large ocean.

Marginal seas add one more complication. A marginal sea is a sea partly enclosed by land or islands at the edge of an ocean, such as the South China Sea at the edge of the Pacific. Britannica notes that even without including its marginal seas, the Pacific is the largest ocean in both surface area and volume, the Atlantic is next, and the Arctic is the smallest. Including or excluding marginal seas changes the numbers, but it does not change the ranking at the top or the bottom.

Why the Area Ranking and the Volume Ranking Agree Here

Area and volume rankings agree for the five oceans as a whole, but they do not have to agree, and the reason they agree is informative. Volume equals area multiplied by average depth. If all five oceans had the same average depth, the volume ranking would simply repeat the area ranking. They do not have the same average depth, so in principle a smaller but much deeper ocean could overtake a larger but shallower one on volume. The numbers show why that does not happen here.

The Pacific combines the largest area with the largest average depth, so no other ocean can catch it on volume. The Atlantic is second by area but third by average depth, behind the Indian Ocean, yet the Atlantic area lead over the Indian Ocean is large enough, 85,133,000 square kilometers against 70,560,000, that the Indian Ocean higher average depth cannot close the volume gap. The Indian Ocean volume of 264,000,000 cubic kilometers stays below the Atlantic volume of 310,411,000 cubic kilometers. At the small end, the Southern Ocean is larger than the Arctic Ocean by area and much deeper on average, so it stays ahead on volume too. The Arctic Ocean is last on all three measures.

There is a general lesson in that arithmetic. A headline that says only “largest” without saying largest by what can hide a real difference. For the Pacific, the headline is safe, because it is largest by area, largest by volume, deepest on average, and holder of the deepest point. For second and third places, the qualifier matters, because the Atlantic is second by area and volume while the Indian Ocean is second by average depth.

The Deepest Point: Challenger Deep and the Mariana Trench

The Mariana Trench is a long, crescent shaped depression in the western Pacific Ocean floor, formed where one tectonic plate slides beneath another. Its deepest section is Challenger Deep, at the southern end of the trench, roughly 200 nautical miles southwest of Guam according to the 2021 NOAA study. The trench is named for the Mariana Islands, and Challenger Deep is named for HMS Challenger, the survey ship whose expedition first sounded great ocean depths in the nineteenth century.

The modern figure of 10,935 meters comes from a careful method. In June 2020, a crewed submersible made repeated transects across candidate deepest areas of Challenger Deep, and the depth was derived from pressure readings corrected for the properties of the water column, atmospheric pressure, gravity, and water level effects. The paper reports the deepest observed seafloor depth as 10,935 meters, plus or minus 6 meters at the 95 percent confidence level, below mean sea level. Earlier surveys using ship based sonar reported different maxima in different basins of the trench, including figures around 10,920 meters, 10,924 meters, 10,984 meters, and 11,034 meters, reflecting different basins, instruments, and corrections.

What does that depth mean in physical terms? At the bottom of Challenger Deep there is no sunlight, the water is cold, and the pressure is roughly a thousand times the pressure at the surface. Life there is sparse and specialized, mostly small invertebrates adapted to cold, darkness, and high pressure, in the hadal zone, the deepest part of the ocean.

Scale Comparisons That Actually Help

Large numbers in millions of square kilometers are hard to picture, so comparisons help if they are honest. Three are used in this article, and each is tied to the table rather than invented for effect.

First, the Pacific share of the world ocean. The Pacific covers about 46.6 percent of world ocean area and holds about 50.2 percent of world ocean volume. That means that if all ocean water were divided into two equal halves, the Pacific alone would hold slightly more than one half. The remaining four oceans together hold slightly less than one half, even though there are four of them. That is a striking way to state the same table, and it is exact enough to check: 669,880,000 divided by 1,335,000,000 is 0.502, or 50.2 percent.

Second, the Pacific against the planet. The world ocean as a whole covers about 71 percent of Earth surface, according to NOAA Ocean Service. The Pacific alone therefore covers a substantial share of the entire planet, not merely a large share of the sea.

Third, the depth comparison with Everest given above. Everest at 8,850 meters against Challenger Deep at 10,935 meters gives a gap of about 2,085 meters, entirely underwater. The comparison works because both figures are vertical distances from sea level, one upward and one downward, so they can be placed on the same scale.

A comparison to avoid is the claim that the Pacific is larger than all the land on Earth combined. That claim appears in some popular sources, and it depends on the boundary definition and on the land figure used, so this article does not rely on it. The table figures are enough.

Why Size Matters Beyond the Record

Size is not just a record for its own sake. A larger ocean has more surface to exchange heat and gases with the atmosphere, more volume to store heat, and more room for currents that move that heat around the planet. NOAA Ocean Service notes that the ocean covers 71 percent of Earth surface and that sea surface temperature is fundamental information for the global climate system, used in weather prediction, atmospheric modeling, and the study of marine ecosystems. The Pacific, as the largest ocean, plays a central part in that system.

The clearest example is the El Nino and La Nina cycle. NOAA explains that during El Nino, temperatures in the Pacific near the equator are warmer than normal, while during La Nina the same area experiences colder than normal temperatures, and that these cycles are caused by multiyear shifts in pressure and wind speeds that affect ocean circulation, global weather patterns, and marine ecosystems. Those shifts begin in the Pacific because the Pacific equatorial region is so wide that changes there can reorganize winds and rainfall far away.

Size also matters for exploration. Mapping 168,723,000 square kilometers of seafloor, much of it several kilometers deep, with ship based sonar is slow and expensive, and satellite methods give good broad coverage but less fine detail. New surveys still revise depth figures by tens of meters, which is why the Challenger Deep depth history shows a spread of estimates narrowing over time as methods improved.

Finally, “smaller” should never be read as “less important.” The Southern and Arctic oceans, though smaller, are disproportionately important for climate because of their cold waters and sea ice. But for the question asked here, which ocean is biggest, the order is settled, and the Pacific is first by a margin that no boundary choice can overturn.

Frequently Asked Questions

What is the biggest ocean in the world?

The Pacific Ocean. It is the biggest by surface area at 168,723,000 square kilometers, biggest by volume at 669,880,000 cubic kilometers, deepest on average at 3,970 meters, and it contains the deepest known point in the oceans, Challenger Deep in the Mariana Trench.

Is the Pacific Ocean bigger than all the other oceans combined?

No, not quite. The Pacific is larger than the Atlantic and Indian oceans combined, but all four other oceans together total 193,211,000 square kilometers, which is more than the Pacific alone. The Pacific does, however, hold just over half of all ocean water by volume, at about 50.2 percent of the world ocean total, so it holds more water than the other four oceans combined.

What is the second biggest ocean?

The Atlantic Ocean is second by both area and volume, at 85,133,000 square kilometers and 310,411,000 cubic kilometers. The Indian Ocean is third on both measures. By average depth, the order of second and third reverses: the Indian Ocean averages 3,741 meters, slightly deeper than the Atlantic at 3,646 meters.

What is the smallest ocean?

The Arctic Ocean is the smallest by area, at 15,558,000 square kilometers, smallest by volume, at 18,750,000 cubic kilometers, and shallowest on average, at 1,205 meters. The Southern Ocean is second smallest by area and volume, but it is much deeper on average than the Arctic Ocean.

How deep is the biggest ocean at its deepest point?

The deepest point in the Pacific Ocean, and in all the oceans, is Challenger Deep in the Mariana Trench, at 10,935 meters below mean sea level according to the 2021 NOAA study, with an uncertainty of 6 meters. Rounded figures of about 11,000 meters, or about 36,000 feet, refer to the same place. Older surveys reported slightly different maxima in different basins of the trench, which is why sources sometimes quote figures between about 10,900 meters and 11,034 meters.

Why do different sources give different sizes for the Pacific Ocean?

Mainly because of boundary choices and marginal seas. A source that defines the Pacific with a southern Antarctic border gives a smaller area, around 165,250,000 square kilometers, than a source that uses the boundary in the table in this article, which gives 168,723,000 square kilometers. Including or excluding marginal seas also changes the total. The ranking is unaffected, because the Pacific lead over the Atlantic is more than 80,000,000 square kilometers, far larger than any boundary effect.

Is the biggest ocean also the deepest ocean everywhere?

No. “Deepest on average” does not mean deep everywhere. Much of the Pacific, like every ocean, consists of abyssal plains several kilometers deep, with shallower continental shelves near coasts and very deep trenches in only a few places. The average depth of 3,970 meters describes the basin as a whole, calculated as volume divided by area, not the depth at any particular spot.

How is this different from asking how many oceans there are?

Counting the oceans asks how the one continuous world ocean is divided and named. Ranking them by size asks how large each named part is once the divisions are agreed. The five oceans used here are the Pacific, Atlantic, Indian, Southern, and Arctic oceans. Changing the count, for example by not recognizing the Southern Ocean as separate, would change the table, but it would not change the fact that the Pacific part is the largest under any common division.

Keep reading: What is Convergent Evolution

Sources & references

• Encyclopaedia Britannica, Ocean: Major subdivisions of the oceans. Table of surface area, volume, and average depth for all five oceans, with data source Eakins and Sharman, Volumes of the World's Oceans from ETOPO1, NOAA National Geophysical Data Center, Boulder, Colorado, 2010; also the statement that even without marginal seas the Pacific is largest in surface area and volume, the Atlantic is next, and the Arctic is smallest; the Southern Ocean definition of waters south of 60 degrees south; and the hypsographic discussion giving Mount Everest at 8,850 meters.
• National Oceanic and Atmospheric Administration (NOAA), Ocean Service: Why do scientists measure sea surface temperature? Ocean covers 71 percent of Earth surface; sea surface temperature and the El Nino and La Nina cycles in the Pacific.
• Greenaway and others, National Oceanic and Atmospheric Administration authors, Revised depth of the Challenger Deep from submersible transects, Deep-Sea Research Part I, 2021, via the NOAA Library repository. Deepest observed seafloor depth 10,935 meters, plus or minus 6 meters at the 95 percent confidence level, below mean sea level; location about 200 nautical miles southwest of Guam; discussion of earlier depth estimates in different basins.