The largest bay in the world is the Bay of Bengal, at about 2.6 million km² (1 million sq mi), bounded by India and Sri Lanka to the west, Bangladesh to the north, and Myanmar and India’s Andaman and Nicobar Islands to the east, with its southern edge drawn from Sri Lanka to Indonesia’s Sumatra. Hudson Bay in Canada is second among water bodies called a bay, at 1.23 million km², and Baffin Bay between Canada and Greenland is third at 689,000 km². Gulfs are bays by another name, so if they are counted too, the Gulf of Guinea (2.35 million km²) moves into second place. It is followed by the Gulf of Mexico (1.55 million km²) and the Gulf of Alaska (1.53 million km²), with Hudson Bay fifth. The table below ranks the ten largest by surface area, using the figures in each body’s Wikipedia article as of October 2026.
| Rank | Bay or gulf | Main countries on its shores | Area |
|---|---|---|---|
| 1 | Bay of Bengal | India, Bangladesh, Myanmar, Sri Lanka | 2,600,000 km² |
| 2 | Gulf of Guinea | Coastal states from Liberia to Gabon, including Ghana, Nigeria and Cameroon | 2,350,000 km² |
| 3 | Gulf of Mexico | United States, Mexico, Cuba | 1,550,000 km² |
| 4 | Gulf of Alaska | United States | 1,533,000 km² |
| 5 | Hudson Bay | Canada | 1,230,000 km² |
| 6 | Baffin Bay | Canada, Greenland (Denmark) | 689,000 km² |
| 7 | Gulf of Thailand | Thailand, Cambodia, Vietnam, Malaysia | 320,000 km² |
| 8 | Gulf of Carpentaria | Australia | 300,000 km² |
| 9 | Persian Gulf | Iran, Saudi Arabia and six other states | 251,000 km² |
| 10 | Gulf of Saint Lawrence | Canada (France’s Saint-Pierre and Miquelon also on its edge) | 226,000 km² |
Two caveats come with this table. First, it only includes bodies of water whose area Wikipedia states, and the bottom of the list is tight: the Gulf of Saint Lawrence, which links the Great Lakes to the Atlantic through the St Lawrence River, takes tenth place by just 3,000 km² over the Bay of Biscay (223,000 km²). Second, the Gulf of Aden would rank seventh on its listed 410,000 km², but Wikipedia’s own editors tag that figure as doubtful because it would make the gulf about as big as the neighbouring Red Sea. It is left out here.
Bay, gulf or bight: why the Gulf of Guinea belongs in the table
In geography, a bay is a body of water partly enclosed by land, and the name a particular one carries is mostly an accident of history. Sailors and map-makers chose “bay”, “gulf”, “bight” or “sea” according to habit and language, not by any size rule. The Bay of Bengal itself was once a gulf: Greek geographers called it the Kolpos Gangetikos, “Gulf of the Ganges”, and Roman writers the Sinus Gangeticus, and European maps used that name for centuries. Its modern name comes from the historical Bengal region, now Bangladesh and the Indian states of West Bengal and Tripura and part of Assam. The Gulf of Guinea, meanwhile, contains two smaller water bodies called bights, the Bight of Benin and the Bight of Bonny. Hudson Bay is classed as an inland marginal sea of the Arctic Ocean. Ranking only the bodies that happen to carry the word “bay” would therefore measure naming customs as much as geography, which is why gulfs are in the table. The guide to bays, gulfs and fjords sets out how the terms overlap.
On the strict “bay” reading, the order is clear. The Bay of Bengal leads, Hudson Bay is the second-largest water body using the term, Baffin Bay is third, and the Bay of Biscay is fourth among those with a listed area, at 223,000 km², just outside the overall top ten.
Torn from Pangaea: the Gulf of Mexico and the Gulf of Guinea
The three largest entries were all made by plate tectonics. When the supercontinent Pangaea broke up along curved fault lines, the continents drifted apart and left large indentations in their coasts. Wikipedia’s article on bays names exactly these three as examples: the Gulf of Guinea, the Gulf of Mexico and the Bay of Bengal.
The Gulf of Mexico shows the process step by step. Before the late Triassic the area was dry land in the middle of Pangaea. Rift valleys opened in the late Triassic and early Jurassic, the crust stretched and thinned through the middle Jurassic, and then it cooled and sank, by 5–7 km in the centre. Kilometres of sediment piled on top since then have pushed the base of that crust 10–20 km below sea level. Today the basin is about 1,500 km wide and holds about 2.4 million km³ of water, bordered by the United States, six Mexican states and Cuba.
The Gulf of Guinea, the north-eastern corner of the tropical Atlantic, runs from Cape Palmas in Liberia to Cape Lopez in Gabon. It is fed above all by the Niger and the Volta. Null Island, the point where the Equator meets the Prime Meridian at zero latitude and zero longitude, lies within it.
Built by the Himalayas: the Bay of Bengal’s sediment fan
The Bay of Bengal’s size also has a second cause: the Himalayas. The collision of the Indian and Eurasian plates raised the mountains, and the Ganges, Brahmaputra and Meghna carry their eroded rock to the bay, nearly 1,000 million tonnes of sediment a year. That load built the Bengal Delta and, offshore, the Bengal Fan. The fan is the largest submarine fan in the world, about 3,000 km long and up to 16.5 km thick, and it covers the whole floor of the bay.
Shaped by ice: Hudson Bay and Baffin Bay in Canada and Greenland
Canada holds two of the ten, and ice helps explain both. Hudson Bay is wide but shallow, averaging about 100 m deep against roughly 2,600 m in the Bay of Bengal. It sits inside the Canadian Shield, under the area once covered by the Laurentide ice sheet. A large gravity anomaly over the bay was long attributed to the crust still recovering from the weight of that ice. The western shore, the Hudson Bay Lowlands, is a peatland of 370,000 km², the largest continuous one in Canada. The bay is largely frozen from mid-December to mid-June. Its water is less salty than the open ocean because about 700 km³ of river water drains into it each year from a basin of 3.86 million km², which reaches into Alberta and the United States.
History put Hudson Bay on the map. Henry Hudson explored it from 2 August 1610 on the Discovery. In 1668 the ship Nonsuch came back loaded with beaver pelts, and in 1670 the English Crown chartered the Hudson’s Bay Company to trade across the whole drainage basin, which became known as Rupert’s Land. The Hudson Bay guide follows that story further.
Baffin Bay, to the north-east, lies between Baffin Island and Greenland. It connects to the Atlantic through the Davis Strait and to the Arctic through the narrow Nares Strait. Ice and icebergs make it unnavigable for most of the year, though a polynya of about 80,000 km² called the North Water opens near Smith Sound each summer. It is named after William Baffin, pilot to the explorer Robert Bylot, who charted it on a voyage completed in 1616. In 1933 its floor produced a magnitude 7.3 earthquake, the largest known north of the Arctic Circle.
Flooded by rising seas: Thailand, Australia and the Persian Gulf
Three of the ten are shallow shelf seas that were dry land at the height of the last ice age, when sea level was about 120 m lower. The Gulf of Thailand averages only 58 m deep, with a maximum of 85 m, so during the Last Glacial Maximum, 26,000–20,000 years ago, it held no seawater at all. It was a freshwater lake on Sundaland, a land bridge that joined the mainland to western Indonesia until about 15,000 years ago. Thailand, Cambodia, Vietnam and Malaysia now share its 320,000 km².
Australia’s Gulf of Carpentaria, 300,000 km² and at most 69 m deep, was likewise dry land 18,000 years ago, along with the neighbouring Sahul Shelf. The Persian Gulf, 251,000 km² and 989 km long, has an average depth of only 50 m. It sits in a basin formed as the Arabian plate is pushed under Iran’s Zagros Mountains, and the sea began flooding it about 15,000 years ago. Iran holds most of the northern shore and Saudi Arabia most of the southern shore, with Iraq, Kuwait, Bahrain, Qatar, the United Arab Emirates and Oman’s Musandam exclave also on its coast.
Lines on the chart: the Gulf of Alaska and the Bay of Biscay
Some bays are big partly because of where their outer limit is drawn. The Gulf of Alaska has no narrow mouth at all. It is simply the curve of Alaska’s southern coast, from Kodiak Island and the Alaska Peninsula to Cape Spencer, closed off by a line across open Pacific water. That open boundary is how it reaches 1.53 million km². The coast is lined with tidewater glaciers, among them the Malaspina and Bering glaciers, Alaska’s largest, and is cut by Cook Inlet and Prince William Sound. Australia’s Great Australian Bight shows the same problem in reverse. The International Hydrographic Organization and the Australian Hydrographic Service define its extent differently, and the area Wikipedia gives, 45,926 km², is far too small for the table.
The Bay of Biscay, eleventh by area, is better enclosed. It is the angle between France’s Atlantic coast and Spain’s north coast, averaging 1,744 m deep with a maximum of 4,735 m. Its shallow continental shelf extends far into the bay and helps explain the rough seas it is known for. The Romans called it the Sinus Cantabrorum, the Cantabrian Gulf, and Spaniards still call its southern part the Cantabrian Sea.
Who owns the water: Bangladesh, India and the 2014 ruling
Policy does not change a bay’s area, but it decides who controls it, and large bays shared by several countries attract boundary disputes. In 2014 a United Nations tribunal settled the maritime boundary between India and Bangladesh. Of the 25,602 km² of disputed Bay of Bengal sea area, it awarded Bangladesh 19,467 km².
Names are political too. In January 2025 a US executive order directed federal agencies to call the part of the Gulf of Mexico in US territorial waters the “Gulf of America”. The International Hydrographic Organization still recognises the name Gulf of Mexico, and the change caused controversy with Mexico.
Rifting continents made the biggest bays, ice and rising seas shaped the shallow ones, and map conventions decide the rest. For the bay at the top of the list, from its cyclones to the Sundarbans, see the full Bay of Bengal guide.