A map of the floor of the whole ocean, sharp from the scale of ocean basins down to single canyons and seamounts, with the great trenches marked at their measured depths. How deep is the sea on average, how much of it is shallow shelf or deep abyss, and how much of it has anyone actually mapped?
We know the shape of the Moon's surface better than the floor of our own sea. Two thirds of the planet is under water, and most of that water is deep: not the blue shallows of the beach, but kilometres of cold, dark sea over plains of mud, ridges of young volcanic rock and trenches deep enough to swallow mountain ranges. I wanted one map of that hidden landscape that stays sharp whether you look at a whole ocean or a single seamount, tells you the depth of any spot you click, and gives plain answers to plain questions. How deep is the sea, really? Where are the deepest places? And how much of the floor has anyone actually measured?
The map below is drawn in your browser from the open terrain tiles first built by Mapzen and now hosted by Amazon. Under the sea they carry the global ETOPO1 and GEBCO compilations and SRTM15+, which combine ship soundings with depths estimated from tiny bumps in the height of the sea surface measured by satellites. Every pixel is a height in metres, negative under the sea. The page turns those numbers into colour and shaded relief as you go. For the numbers I used the same tiles at their coarsest level, a world grid of 4,096 by 4,096 cells, about 9.8 km across at the equator, with every cell weighted by its true area.
Line up every square kilometre of the sea floor from the shallowest to the deepest and the ocean turns out to be anything but a bowl. The average depth is 3,675 m and the median 4,089 m: half the sea floor is deeper than four kilometres. The shallow continental shelves, the drowned edges of the continents less than 200 m down where most fishing, oil and wind farms are, cover only 7.7% of it. The continental slopes and rises and the shallower ridges between 200 and 3,000 m take 17%. Then come the abyssal plains and hills between 3,000 and 6,000 m: 74% of the floor, 268.8 million km², more than half of the whole planet's surface. The hadal zone, the trenches below 6,000 m, is only 1.0% of it, about 3,632,872 km² on this grid.
How much of the sea floor lies at each depth
Share of the ocean floor in each depth band, from the zoom 4 grid weighted by true cell area. Hover for areas and the share of the whole Earth's surface.
Seen against the whole planet, the Earth's surface has two levels, not one. A histogram of every height and depth has two humps: one just above sea level, where 10.0% of the surface lies between 0 and 250 m up, and a bigger, broader one around 4,000 to 5,000 m down, where the ocean crust sits. The sea covers 71.2% of the Earth on this grid, and the average sea floor lies 4.6 times deeper than the average land stands high (801 m). The two levels are two different kinds of crust: thick, light continents floating high, and thin, dense ocean floor riding low.
The two levels of the Earth
Share of the Earth's whole surface in each 250 m step of height or depth (sea floor in blue, land in sand). Hover for values.
Grouping the International Hydrographic Organization's sea areas into five oceans, the Pacific is the biggest (47% of all sea) and the deepest, averaging 3,943 m. The Indian Ocean averages 3,775 m, the Atlantic 3,606 m and the Southern Ocean 3,213 m. The Arctic is the odd one out: 1,205 m on average and a median of only 325 m, because two fifths of it is shallow continental shelf, much of it off Siberia. Marginal seas can be shallower still: the North Sea averages 76 m, the Baltic 60 m and the Persian Gulf 33 m, while the Philippine Sea averages 4,361 m.
Average depth of each ocean, and its deepest known place
Mean depth of each ocean on the 10 km grid (bars), with the deepest point found by published sonar surveys. Hover for medians and the grid's own deepest cell.
The deepest places are long, narrow trenches where one plate of ocean floor bends down under another. The deepest of all is the Challenger Deep at the southern end of the Mariana Trench, south-west of Guam. Its depth has been argued over for seventy years; the most careful estimate, from pressure sensors on crewed submersible dives, is 10,935 m, give or take 6 m. Put Mount Everest (8,849 m) on the floor there and its summit would still be 2,086 m under water, deeper than most submarines can go.
A slice through the Mariana Trench, with Everest for scale
Height of the sea floor along longitude 142.588° E from 14.5° N to 8° N, through the Challenger Deep (zoom 4 grid, sampled every km). The dashed line is the measured depth of the Deep; Everest is drawn standing on it. Vertical scale exaggerated.
A 10 km grid cannot see the very bottom of features only a few kilometres wide, so it understates the trenches. Its deepest cell in the Mariana Trench is 10,264 m, 671 m short of the truth. In fact the deepest cell of the whole grid is not there at all but in the Tonga Trench (10,467 m), whose deepest place, the Horizon Deep, has been measured at 10,816 m. The table compares the grid with published surveys for 14 of the deepest places. In 4 of them the grid is deeper than anything measured there, which a 10 km average should not be: those cells carry errors from old soundings or from the satellite estimates, a reminder that the global maps are smoother and less certain than they look.
The deepest places: measured depth and what the 10 km grid sees
Published depth of each trench's deepest point (dark dot, sources in the notes) and the deepest cell of the zoom 4 grid along the trench (open dot). Click to fly there.
Every coastal state claims an Exclusive Economic Zone reaching up to 200 nautical miles out to sea. Using the Marine Regions boundaries, including joint regimes and disputed claims, national waters cover 39% of the sea on this grid, and the high seas beyond them 61%. National waters are shallower on average (2,731 m against 4,273 m), because they hold the shelves, but they also hold the trenches, which hug island arcs: 37% of the sea floor deeper than 6,000 m is in someone's zone. The deepest cell of any zone on the grid is in Tonga's; the Challenger Deep itself lies in the zone of the Federated States of Micronesia, just south of the waters of the United States territory of Guam.
The deepest national waters
Deepest cell of the zoom 4 grid inside each Exclusive Economic Zone (Marine Regions). Click to fly there.
The sea floor is studded with volcanoes that never reached the surface. The Marine Regions gazetteer, which carries the official undersea feature names, lists 2,000 named seamounts, 219 guyots (flat-topped seamounts, planed off by waves when they stood at sea level and since sunk) and 330 knolls. Turn on the seamounts layer to see them. That is only a sliver of what is there: a census from satellite gravity data by Kim and Wessel found 24,646 likely seamounts big enough to show up from space, around 9.7 times as many as have names, and estimates for the smaller ones run far higher. Most have never been surveyed by a ship.
Almost everything on this map away from the coasts and the ships' tracks is an estimate. Satellites measure the height of the sea surface, which bulges by a few metres over a seamount and dips over a trench, and models turn those bumps into depths, sharp only to around ten kilometres or more. Mapping the floor properly takes ships with multibeam sonar, slowly sweeping a strip at a time. The international Seabed 2030 project, which compiles the GEBCO grid, reported in 2026 that 28.7% of the ocean floor is now mapped to modern standards, up from 27.3% a year earlier. That leaves about 259 million km² known only roughly, an area larger than all the land on Earth.
Share of the sea floor mapped to modern standards
Seabed 2030 and GEBCO, GEBCO_2026 grid.
28.7% mapped · 71.3% still to go. At last year's pace of 1.4 percentage points a year the job would take about 51 more years; finishing by 2030 would need about 17.8 points a year.
Depths. The AWS Terrain Tiles store height in the red, green and blue of each pixel (height = R × 256 + G + B ÷ 256 minus 32,768 m). The map decodes them live at every zoom. For the statistics I mosaicked the 4,096 by 4,096 grid at zoom 4 (9.8 km at the equator, 4.9 km at 60°), weighted each cell by its exact area on a sphere and by the share of it that is sea, and replaced 13 corrupt cells by the median of their neighbours. The Web Mercator grid stops at 85° N, so the Arctic Ocean around the Pole (0.9 million km²) comes from ETOPO10, a coarser version of ETOPO1.
What counts as sea. Everything outside Natural Earth's land and lakes that joins the world ocean; the Caspian is a lake and is left out, the Black Sea is in. Sea cells whose 10 km average is above sea level count as 0 m deep. The floating ice shelves of Antarctica count as land, so the sea under them is missing. Oceans are the IHO's sea areas grouped into five (the Arctic includes the Greenland, Norwegian and Barents Seas and Baffin and Hudson Bays; the Southern Ocean is the sea south of 60° S). National waters are Marine Regions' Exclusive Economic Zones, joint regimes and overlapping claims.
Checks. Natural Earth's hand-drawn bathymetry polygons give almost the same picture: 334.4 million km² deeper than 200 m against 335.1 million on the grid, and 181.2 million against 191.1 million deeper than 4,000 m. The grid's average depth of 3,675 m and volume of 1.33 billion km³ are close to the 3682.2 m and 1.332 billion km³ that Charette and Smith calculated from a finer grid.
Limits. A 10 km grid smooths the sea floor: trenches look shallower and seamounts lower than they are, and the shares in each depth band are good to a point or so, not to the decimal. Most of the floor is estimated from satellites rather than measured. The published depths of the deepest places come from different surveys of different ages and accuracies; the ones without a stated uncertainty are rougher. The named seamounts are only those that someone has named, which says as much about where research ships have been as about the sea floor.