What is the tallest mountain above sea level?

Everest reaches 8,849 metres above sea level, a figure revised upward slightly in 2020 by a joint Chinese and Nepali survey. The qualifier in the question is doing real work, though, because there are two other mountains that beat it on different measures.

Measured from its own base, Mauna Kea in Hawaii runs about 10,200 metres from the sea floor to its summit, of which only 4,200 are above water. And measured as distance from the centre of the Earth, the winner is Chimborazo in Ecuador - the planet bulges at the equator, so a peak sitting almost on it starts from further out. Chimborazo's summit is roughly two kilometres further from the Earth's centre than Everest's.

Everest is also still growing, by a few millimetres a year, as India continues to drive into Asia. The mountain is made partly of marine limestone: the summit rock formed on a seabed, full of the shells of animals that lived in the ocean that used to be there.