What is the tallest mountain on Earth measured from base to summit?

Mauna Kea is the tallest mountain on Earth when measured from its true geological base to its summit. Much of the Hawaiian volcano is submerged beneath the Pacific Ocean, so its full rise from the ocean floor is more than 10,000 metres, or roughly 33,500 feet.

Above sea level, Mauna Kea reaches 4,205 metres—far below Mount Everest’s 8,849-metre summit. That difference explains why Everest is the world’s highest mountain by elevation above sea level, while Mauna Kea wins the base-to-summit comparison. The exact base can be defined in different ways, so published totals vary slightly, but the ranking remains the same.

Mauna Kea is a dormant shield volcano on Hawaii’s Big Island. Its broad shape was built by repeated flows of relatively fluid basaltic lava, and its summit is famous for exceptionally clear, dry air. Those conditions have made it one of Earth’s premier astronomical observing sites, with major observatories operated near the summit. Denali is another frequent mix-up: it has a greater rise above its immediate surroundings than Everest, but not as great a base-to-summit height as Mauna Kea.