Which mountain is the tallest from base to summit?

Mauna Kea is the tallest mountain from base to summit, rising about 10,211 metres from its submarine base on the Pacific Ocean floor to its summit.

Only about 4,207 metres of Mauna Kea stands above sea level, so Mount Everest remains the highest mountain above sea level. Mauna Kea's lower slopes are hidden beneath the ocean, which is why its full height is often overlooked. It is a dormant volcano on Hawaii Island and one of several large shield volcanoes that formed the Hawaiian Islands.

The summit of Mauna Kea is an exceptional astronomical location. Its high elevation, dry air, stable atmosphere, and low light pollution support major observatories, including facilities operated by international research groups. The mountain is also culturally significant to Native Hawaiians, and observatory development has been the subject of longstanding debate.

Mauna Kea last erupted roughly 4,600 years ago. Mauna Loa, another Hawaiian volcano, is larger by volume and is often confused with Mauna Kea. The answer therefore depends on the measurement used: elevation above sea level, base-to-summit height, or total volcanic volume.