What is the highest mountain measured from its base?

The highest mountain measured from its base is Mauna Kea. This dormant shield volcano on Hawaiʻi rises about 10,203 metres from the Pacific Ocean floor to its summit, although only about 4,207 metres stands above sea level.

That measurement explains why Mauna Kea can beat Mount Everest in a different kind of height contest. Everest is the highest summit above sea level, while Mauna Kea's underwater base gives it a much greater total rise from foundation to peak. The exact figure varies because a mountain's “base” is not defined in one universally agreed way.

Mauna Kea began forming roughly one million years ago over the Hawaiian hotspot and last erupted several thousand years ago. Its summit is unusually dry and stable, making it one of the world's premier locations for astronomy. Telescopes operated there include facilities built by several countries, though the summit is also sacred to Native Hawaiians and remains the subject of cultural and environmental debate.

Mauna Loa is a frequent mix-up. It is larger by volume, but Mauna Kea is the standard answer for the tallest mountain measured from seafloor base to summit. Chimborazo instead reaches farther from Earth's centre because the planet bulges at the equator.