It’s easy to mistake seas and oceans for one another. You can’t tell the difference by looking at them, leading most to falsely assume that they’re the same thing. To end the “Sea vs Ocean” debate once and for all, this article highlights the four main differences between them.

Atlantic Ocean (left) vs. Caribbean Sea (right)

Credit Left: Tiago Fioreze, CC BY-SA, Right : Kijan Ay, CC BY 3.0

Main Differences

There are four main differences that make the “Sea vs Ocean” question easy to answer:

  • Size: Oceans are much larger than seas.
  • Location: Most seas are partially surrounded by land, while oceans are not. Seas are also located within oceans.
  • Depth: Oceans are much deeper than seas.
  • Quantity: There are 28 seas and only five oceans in the world.

What is a Sea?

A sea is a large body of saltwater that borders a landmass. Most seas, like the Mediterranean Sea, are only partially surrounded by land. There are also some seas, like the Caspian Sea, that are “landlocked” or completely surrounded by land.


There is no official minimum size for a sea, but seas are always smaller than oceans.
Seas come in very different shapes and sizes. For example, at 137,000 square kilometers in size, the Adriatic Sea is the smallest sea in the World. At over 5.5 million square kilometers in area, the Philippine Sea is the World’s largest sea!


Seas can be found connecting all of the planet’s seven continents. Most seas are found on the coastline and are actually a part of the ocean.


Seas usually aren’t deeper than 2000 meters. Many animals, including some animals found in the Mariana Trench, don’t even live at depths above 2000 meters. Instead, if these animals rise to the surface without special precautions, the lack of water pressure can be extremely damaging and often fatal to the fish.

What is an Ocean?

The “sea vs ocean” debate is so confusing because sailors used to refer to our oceans as “The Sea.” Over time, scientists discovered that the sea is really grouped into bodies of water called oceans.
There are five official oceans:

  1. Pacific
  2. Atlantic
  3. Indian
  4. Arctic
  5. Southern

Unlike seas like the Caspian, there are no landlocked oceans. In fact, every ocean shares at least one border with every other ocean.


Unlike seas, even the smallest ocean is too large to be even partially contained by any land mass smaller than an entire continent. Instead, the oceans are the ones surrounding the continents.

The Arctic Ocean is our smallest ocean, spanning ~5.5 million square kilometers. The Pacific Ocean is our largest ocean at ~165.2 million square kilometers. That means it covers over 30% of Earth’s surface by itself!


Since oceans take up most of the world, most people don’t consider them to have a specific location. Instead, oceans are usually considered the “background” of our world maps.


An average spot on the Ocean floor is over 3500 meters, or over 12,000 feet, deep. The ocean floor is so deep that light can’t reach the bottom! Animals that live down there have to survive in total darkness.

Since the ocean is so deep, most animals that live on the surface aren’t able to survive at the bottom. Cuvier’s Beaked Whales are the deepest-diving species in the World, and even they can’t reach the ocean floor.


How many seas are there?

There are 28 officially listed seas in the World, found on all seven continents. These seas were mapped by the International Hydrographic Organization (IHO), the group responsible for mapping major bodies of water on Earth.

Are seas the same as gulfs?

Not quite. Gulfs are the parts of a sea that are surrounded by land.

For example, the Persian Gulf is surrounded from all sides by water except an opening in the East which leads to the rest of the Sea of Oman. Gulfs are arts of seas, and seas are parts of oceans.

How many gulfs are there?

There are 62 officially listed gulfs in the World, the largest and deepest of which is the Gulf of Mexico. These gulfs come in many different shapes and sizes.

Are seas and bays the same?

Seas and bays are two different things. Bays and gulfs are both parts of a sea. Unlike a gulf, a bay is a part of the sea that causes the land to curve inward. For example, the Bay of Bengal is surrounded from the West, North, and East by a curved land mass.

How many bays are there?

Depending on your definition, there can be hundreds of bays, but the International Hydrographic Organization has assigned data codes to 9 of these bays. These bays include the Hudson, Baffin, James, Palk, Bengal, Biscay, Fundy, Bristol, and Korean Bays.

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