The tallest mountain from base to summit is not Mt. Everest but instead Mauna Kea on the island of Hawaii. Everest stands 29,035 feet above sea level but Mauna Kea is ~33,500 feet tall with over half of its height underwater. – WTF Fun Facts
Source: https://www.businessinsider.com/earths-tallest-mountain-is-hawaii-2015-6