How tall is a mountain, really?

Everest wins above sea level. Mauna Kea wins from base to summit.

≈4,205 m above sea level · ≈10,211 m from ocean-floor base to summit

Both numbers are correct. They answer different questions.

Depends on the measurement reference

Why this is interesting

Mount Everest is the highest mountain above sea level. But much of Mauna Kea is hidden underwater.

Start measuring at Mauna Kea's base on the deep ocean floor instead of at the shoreline, and you get a different — and much larger — number. That doesn't contradict Everest's record. It answers a different question.

How this measurement works

Elevation is height measured from a sea-level reference. On that measure, Mauna Kea's summit is about 4,205 m above sea level.

Base-to-summit height is the vertical distance from a chosen physical base up to the summit. USGS describes Mauna Kea extending about 6,000 m below sea level to meet the deep ocean floor, for a total height of nearly 10,211 m.

10,211 m is not Mauna Kea's elevation. And "base" isn't defined the same way for every mountain — which is why base-to-summit figures need to say where they start.

Three mountains. Three ways to be the tallest.

Ask which mountain is the world's tallest, and you might get three correct answers. It all depends on where you start measuring.

1. Mount Everest — Highest above sea level: 8,848.86 m above sea level; Everest holds the conventional record for the highest summit above sea level. This is the elevation measurement most people mean when they ask about the world's highest mountain.
2. Mauna Kea — Tallest from base to summit: ≈10,211 m from underwater base to summit; Only about 4,205 m rise above sea level. Much of this Hawaiian volcano lies beneath the Pacific Ocean.
3. Chimborazo — Farthest from Earth's centre: ≈6,268 m above sea level · summit ≈2.1 km farther from Earth's centre than Everest's; Earth bulges around the equator because of its rotation. Chimborazo (opens external site), in Ecuador, lies close to that bulge, giving it the greatest distance from Earth's centre of any mountain summit.
The takeaway: The mountains didn't change. The starting point of the measurement did.

See the math

Summit elevation: ≈4,205 mSource value; Above sea level (USGS)
Extends below sea level: ≈6,000 mSource value; Down to the deep ocean floor (USGS)
Base-to-summit height: nearly 10,211 mSource value; USGS total height — not an elevation

How certain is this?

Authoritative reference values · measurement depends on reference point. Both figures come from USGS. They measure from different starting points, so they are not interchangeable.

These are two different measurements of the same mountain and are kept as separate properties: summit elevation is measured from sea level, base-to-summit from the ocean floor.

Sources & further reading

USGS
Mauna Kea(opens external site)
USGS
How big are the Hawaiian volcanoes?(opens external site)
Mauna Kea 4,205 m above sea level
USGS
How big are the Hawaiian volcanoes?(opens external site)
About 6,000 m below sea level to the ocean floor
USGS
How big are the Hawaiian volcanoes?(opens external site)
Total height nearly 10,211 m
USGS
How big are the Hawaiian volcanoes?(opens external site)
Summit elevation and ocean-floor-to-summit height
NOAA National Ocean Service
What is the highest point on Earth as measured from Earth's center?(opens external site)
Three ways to be tallest: Everest above sea level, Mauna Kea base to summit, Chimborazo farthest from Earth's centre (~2.1 km beyond Everest)
NASA Earth Observatory
Chimborazo and Tungurahua, Ecuador(opens external site)
Independent support for Chimborazo and the equatorial bulge

Follow this rabbit hole

Where does a volcano begin?Mauna Loa doesn't stop at the shoreline—or even at the seafloor.

Keep going

Back to the converter Explore the measurement library