Olympus Mons is a large on. As measured by the (MOLA), it is 21.1 kilometres (69,000 ft) or, more precisely, 21.287 kilometres (69,840 ft) high, about 2.5 times the of. It is Mars's tallest volcano, its tallest planetary mountain, and is approximately tied with on as the tallest mountain currently discovered in the Solar System. I.