Wonders of Nature Earth Science No background needed About 6 min read

Is Everest Really the Tallest Mountain in the World?
― Measured from the Earth's centre, first place goes to a mountain near the equator

"The tallest mountain in the world is Everest." That is not wrong. But it comes with a condition: "measured from sea level." Move the ruler, and first place can go to a Hawaiian mountain or a South American one.

Published: 2026.10.14 Difficulty: ★☆☆ (no background needed) The only maths is in the fold-out section at the end

First, picture this scene

Imagine a quiz show asks, "What is the tallest mountain in the world?" Almost everyone would answer "Everest." Its height is about 8849 metres. Textbooks and atlases all say so.

But ask someone in Ecuador, in South America, and they may tell you, "The summit closest to space is our Chimborazo." Its elevation is about 6270 metres. That is more than 2500 metres lower than Everest.

How can a lower mountain be "closest to space"? Neither person is wrong. They are measuring height with different rulers.

"Tallest" changes for just two reasons

Nobody has fixed "where to measure from"

The "elevation" we normally use is height measured from sea level, taken as 0. But you can also measure from the foot of the mountain, or from the centre of the Earth. Change the starting point and the ranking changes too.

The Earth bulges at the equator

The Earth spins, so the area around the equator bulges slightly outward. Near the equator, sea level itself is farther from the Earth's centre. A mountain standing there starts with a built-in head start.

Look at these two in turn, and it becomes clear when Everest comes first and when it does not.

Let's try three rulers

Let's consider three rulers for measuring height. The first measures from sea level, the second from the foot of the mountain, and the third from the centre of the Earth. Figure 1 compares three famous mountains with these three rulers.

With the first ruler, "from sea level," Everest's roughly 8849 metres is the clear winner. Hawaii's Mauna Kea is only about 4207 metres.

But Mauna Kea is a mountain that only pokes its head out of the sea. Its base is said to lie on the seafloor, about 6000 metres below the surface. Measured with the second ruler, "from the foot," its height tops 10,000 metres. Everest's base sits on a high plateau, so its height from the foot is much smaller than 8849 metres.

Figure 1: Three mountains measured with three rulers. In the left chart (from sea level), Everest is first. In the middle chart (from the foot), Mauna Kea, which rises from the seafloor, is first. The dotted frame shows that Everest's height from its foot is less than 8.85 km. In the right chart (from the Earth's centre), Chimborazo, which has the lowest elevation of the three, is first.

The equatorial bulge pushes a lower mountain up

Why does Chimborazo win with the third ruler? The key is the shape of the Earth. The Earth turns once a day, so the area around the equator bulges outward. The radius at the equator is said to be about 21 kilometres longer than the radius at the North Pole.

Chimborazo lies only about 1.5 degrees south of the equator. That is almost the very top of the bulge. Everest, on the other hand, sits at about 28 degrees north. There, sea level dips about 4.7 kilometres closer to the centre than sea level at the equator.

Use the slider in Figure 2 to move the mountain north from the equator. The farther north you go, the closer sea level gets to the centre, and the more elevation you need to match Everest's summit. Right on the equator, a mountain of about 4.2 kilometres is enough. At 60 degrees north, you would need one over 20 kilometres tall.

Latitude of the mountain 28 degrees → elevation needed to match Everest's summit 8.9 km Move the slider and the height needed at that latitude (the vertical band) changes

Figure 2: Where a mountain stands (latitude) and the elevation it needs to match Everest's summit. The solid line sloping down to the right is sea level, which gets closer to the Earth's centre toward the north. The dotted line at the top is the height of Everest's summit. The triangle in the middle is Everest, and the vertical band shows the height needed at the latitude chosen with the slider. Chimborazo, the dot at upper left, rises above the dotted line.

Chimborazo's summit is about 6384 kilometres from the Earth's centre. Everest's summit is about 6382 kilometres. It loses by more than 2500 metres in elevation, yet it wins by about 2 kilometres in distance from the centre.

💡 So is "closest to space" true too?

In the sense of being farthest from the Earth's centre, Chimborazo's summit is said to be the most "outward" point on the ground. But how thin the air is depends almost entirely on elevation. Breathing is still harder on Everest.

Summary

"The tallest mountain in the world is Everest" is the right answer under the convention of measuring from sea level. Measured from the foot, Mauna Kea is first. Measured from the Earth's centre, Chimborazo is first. Chimborazo wins because the spinning Earth bulges at the equator, pushing sea level itself outward.

"Tallest" is not a property of the mountain.
It depends on where you place the ruler.

Why the Earth is round, and how flattened it is, is explained in "Why Is the Earth Round?". Why fossils of sea creatures turn up on mountaintops is explained in "How Did Shell Fossils Get to the Top of a Mountain?"

🧪 Check the different rulers with an atlas

Find Everest, Chimborazo and Mauna Kea in an atlas or on a globe, and read off each one's latitude.
Set the slider in Figure 2 to the latitude of each of the three mountains, and see how far sea level dips toward the centre at each place.
Try the same for Japan's Mount Fuji (about 35 degrees north, elevation about 3776 metres). How many more kilometres would it need to match Everest's summit?

A globe does not reproduce the flattened shape caused by rotation, so it is best to check the bulge with numbers.

For those who want to know more ― terms, formulas and links to textbooksEach part is labelled by level, from junior-high science to university-level courses

How to read the labels that follow

Junior highCovered in junior-high science
High schoolCovered in high-school earth science or physics
High school+Advanced high-school material, or textbook sidebar content
UniversityNot taught in high school; university-level geodesy
ResearchNot yet taught as settled knowledge, even at university; what researchers are studying now

Junior highTerms: this phenomenon has names

Elevation: height measured with average sea level as 0. The "height" used on maps and in mountaineering is usually this.
Relative height: the height from the foot of a mountain to its summit. For a mountain that rises from the seafloor, like Mauna Kea, it is far greater than the elevation.
Spheroid (ellipsoid of revolution): the shape made by rotating an ellipse around its axis. The Earth is close to a spheroid bulging slightly toward the equator.

Junior highHigh schoolCheck with a formula: how many kilometres is a summit from the Earth's centre?

We calculate the distance from the summit to the Earth's centre for Everest and Chimborazo, and compare them.

⓪ The underlying formula

In symbols	r ＝ a − ( a − b ) × sin²φ ＋ h
In words	Summit's distance from the centre ＝ equatorial radius −（difference between equatorial and polar radius）×（square of the sine of the latitude）＋ elevation
Where it comes from	The sea-level radius (an approximation) when the Earth is treated as a spheroid flattened by its spin, plus the height above sea level. The equator bulges because gravity and the centrifugal force of rotation balance

Symbols: r is the summit's distance from the centre, a is the equatorial radius, b is the polar radius, φ is latitude, and h is elevation. All units are kilometres (φ is in degrees).

① Starting values

Equatorial radius a	about 6378.1 km
Polar radius b	about 6356.8 km
Everest: latitude and elevation	about 28° N, about 8.85 km
Chimborazo: latitude and elevation	about 1.5° S, about 6.27 km
Square of the sine of 28°	said to be roughly 0.22
Square of the sine of 1.5°	said to be roughly 0.0007

② Let's calculate

Difference between equatorial and polar radius	6378.1 − 6356.8 ＝ 21.3
How far sea level dips at Everest's location	21.3 × 0.22 ≒ 4.7
Sea-level radius at Everest's location	6378.1 − 4.7 ＝ 6373.4
Everest summit's distance from the centre	6373.4 ＋ 8.85 ＝ 6382.25
How far sea level dips at Chimborazo's location	21.3 × 0.0007 ≒ 0.015
Sea-level radius at Chimborazo's location	6378.1 − 0.015 ≒ 6378.1
Chimborazo summit's distance from the centre	6378.1 ＋ 6.27 ＝ 6384.37
Difference between the two summits	6384.37 − 6382.25 ＝ 2.12

Chimborazo's summit turns out to be about 2.1 kilometres farther from the Earth's centre. The difference in the bulge of sea level (about 4.7 km) outweighs the difference in elevation (about 2.6 km). The dotted line and vertical band in Figure 2 are drawn with this formula too.

High schoolHigh school+Why does the equator bulge?

High schoolThe Earth rotates, so centrifugal force acts on everything at the surface. It is strongest at the equator, which is farthest from the axis of rotation, and zero at the poles. Over a long time, seawater and rock settle onto a surface perpendicular to the combined force of gravity and centrifugal force. The result is a shape that bulges outward at the equator.

High school+The degree of flattening is expressed by the flattening ratio, which is said to be about 1 in 298 for the Earth. Real sea level is also uneven, because of uneven mass distribution underground. This uneven surface is called the geoid, and elevation is properly measured from the geoid.

UniversityHow "height" is defined in geodesy

In geodesy, height above the spheroid that approximates the Earth (the reference ellipsoid; Japan uses the internationally defined GRS80 ellipsoid) is called ellipsoidal height, and height above the geoid is called elevation. The difference between the two is the geoid height. The formula above is an approximation that expands the geocentric radius of the ellipsoid in terms of latitude, and it leaves out things such as the difference between geodetic and geocentric latitude.

📖 Derivation of the formula and further reading: Earth ellipsoid (Wikipedia, in Japanese) ／ Chimborazo (Wikipedia, in Japanese)

ResearchWhat is still not well understood

The summit's height itself is changing. Everest is said to be still rising slowly, because the Indian continent keeps pushing against Asia. Erosion and earthquakes lower it, though, and the net change is still debated.
How much snow and ice to include. The thickness of snow and ice on a summit changes with the season and the year. Even for Chimborazo, surveys in different years give elevations that differ by a few metres.
Where is the foot on the seafloor? Mauna Kea is said to press the seafloor down under its own weight. The value of its relative height changes a lot depending on where you call the "foot."

So the content of this article is also "an explanation of what is known so far." Mountain heights have been rewritten each time measuring technology has advanced.

Links to textbooks (by level)

Level	Subject / unit	Where in this article
Junior high	Science: changes in the land	Mountain height, the word "elevation"
High school	Basic Earth Science: shape and size of the Earth / Physics: centrifugal force	Why the equator bulges
High school+	Earth Science: flattening, geoid	Sea level as the starting point of elevation
University	Geodesy	Difference between ellipsoidal height and elevation
Research	Geodesy, geophysics	Mountain uplift, sinking of the base
―	Links to daily life	Car navigation and smartphone positioning also use height above the ellipsoid

References and sources

Wikipedia, "Earth ellipsoid" (地球楕円体), in Japanese
Wikipedia, "Chimborazo" (チンボラソ), in Japanese
National Astronomical Observatory of Japan (国立天文台), ed., Rika Nenpyo (理科年表, Chronological Scientific Tables), Maruzen Publishing (shape and size of the Earth; heights of major mountains)
Geospatial Information Authority of Japan (国土地理院), explanatory materials on the "Basics of Geodesy" (測地学の基礎) (elevation, ellipsoidal height, geoid height)
Joint announcement of Everest's height by the Chinese and Nepali governments (2020, 8848.86 metres)

※This article is a general-audience science explainer. The figures given are rough guides to help you understand the mechanism. Mountain heights differ by a few metres depending on the year and method of survey.