Which mountain is the tallest when measured from base to summit?

Mauna Kea, a dormant volcano on Hawaiʻi Island, is often called the tallest mountain on Earth when measured from base to summit. Its summit is 4,207 meters above sea level, but because it rises from the ocean floor, its total height is about 10,200 meters. That makes it taller than Mount Everest in the base-to-peak measurement, even though Everest is higher above sea level. Mauna Kea’s summit is also famous for major astronomical observatories because of its dry, clear atmosphere.