Which mountain has the greatest height from its base to its summit?

Mauna Kea has the greatest height from its base to its summit.

This dormant shield volcano rises from the Pacific Ocean floor near Hawaiʻi. Its summit reaches about 4,207 meters above sea level, but the volcanic mountain extends roughly 6,000 meters below sea level. Measured from its underwater base to its peak, Mauna Kea is about 10,200 meters tall—taller than Mount Everest’s 8,848.86-meter elevation above sea level.

The answer depends on how height is measured. Mount Everest is the highest mountain above sea level, while Mauna Kea is generally described as the tallest from base to summit. Because an underwater mountain’s exact base is difficult to define, published totals can vary slightly.

Mauna Kea formed from repeated volcanic eruptions as the Pacific Plate moved over the Hawaiʻi hotspot. Its high, dry summit is also famous for astronomy: observatories there benefit from stable air, low humidity, and limited light pollution.