How Deep Is the Ocean Really? Deeper Than Mount Everest Is Tall

How deep is the ocean really? At the deepest spot, around 10,935 meters (about 35,876 feet). That number is hard to picture. Try this: take Mount Everest, the tallest mountain on Earth. Flip it upside down. Drop it into the deepest part of the ocean. The summit would not break the surface. There would still be 2 kilometers of water on top of it. That is the Mariana Trench in the Pacific. We will show you how deep the ocean really is, how brutal the pressure gets down there, and why more people have walked on the Moon than have stood at the deepest point on Earth.

How deep is the ocean at its deepest point?

The deepest known spot in the ocean is called Challenger Deep. It sits at the southern end of the Mariana Trench, a long crescent-shaped scar in the floor of the western Pacific, just east of the Mariana Islands. A 2020 submersible expedition measured it at 10,935 meters (about 35,876 feet) deep. Older sonar measurements went as high as 10,984 meters. Either way, you are looking at over 6.8 miles straight down. For context: a commercial jet flies at around 11 km altitude. The ocean here is almost as deep as a plane is high.

On average, the ocean is not that deep. The mean depth of all oceans is around 3,682 meters (12,080 feet). Still huge. But the Mariana Trench is special. It runs about 2,550 km (1,580 miles) long and up to 69 km wide. A real gash in the seafloor.

Mount Everest fits inside. With room to spare.

Mount Everest stands at 8,848.86 meters (29,032 feet). Round it to 8,849 meters. If you took the entire mountain and dropped it into the Mariana Trench, the summit would still be more than 2,000 meters underwater. You would need to stack a second mountain about as tall as Mount Hood on top before reaching the surface. Plot twist: the tallest mountain on Earth is shorter than the deepest hole in the sea.

And that is even though Everest already starts on a high plateau. When you compare mountains and trenches fairly, the ocean wins. Easily.

Why the pressure down there crushes everything

Water is heavy. The more of it stacked above you, the harder it presses down. In the Mariana Trench, that is almost 11 km of water. The pressure at the bottom is around 1,127 bar. At sea level, the air around you is about 1 bar. So we are talking about 1,100 times normal atmospheric pressure.

What does that look like in real life? A foam coffee cup sent down on the outside of a sub gets crushed to the size of a thimble. Glass cracks. Steel has to be very thick to not implode. And yet life still exists down there. Fish, shrimp, jellyfish, and tiny microbes survive at full crushing pressure. Their bodies push back from the inside with the same force, so they do not get squashed.

More people have walked on the Moon than reached this spot

Here is the number that surprises most people. Only about 27 humans have ever reached the floor of Challenger Deep. Twelve astronauts have walked on the Moon. Twenty-four total flew to the Moon, including six who orbited it without landing. For decades, more people had been around the Moon than had touched the deepest point on Earth. The Challenger Deep visit count only recently passed the moonwalker count.

The most famous trip down: filmmaker James Cameron, who in March 2012 became the first person to dive solo to the bottom of the Mariana Trench. He hit 10,908 meters and stayed on the seafloor for around four hours. His sub was named Deepsea Challenger. Before him, Jacques Piccard and Don Walsh got there first in 1960. After Cameron, billionaire investor Victor Vescovo dove down 15 times alone in his sub Limiting Factor.

Want to test your sense of scale? Try our geography estimation questions. Over 80 questions, free, runs in your browser, perfect for your next road trip.

We know more about the Moon than the seafloor

This sounds insane, but it is true. The Moon has been fully mapped. As of 2024, only about 26 percent of the seafloor has been mapped in high resolution. The rest is rough estimate, pieced together from satellite gravity data. So three quarters of the floor under our oceans is still a fuzzy guess.

The reason is simple. Light does not travel far in water. Radio waves do not either. To map depth, you need sonar or a sub. Both are expensive and slow. It is easier to point a telescope at Mars than to see through 11 km of water. The deepest point on Earth is right under us, but harder to reach than space.

If scale games are your thing, also check out our post on how tall the tallest mountain in the world really is. Spoiler: you are looking at Everest the wrong way.

The ocean goes deeper than your imagination can keep up with. Deeper than the tallest mountain, darker than any cave, colder than any winter. And we have only mapped a quarter of it. For more aha-moment geography facts, try our geography estimation questions.