Exploratour - Comparing the Surfaces of Earth and Mars
The graph to the left compares the size of the highest peaks of Earth and Mars. Mars Global Surveyor measured the size of Olympus Mons. The altitudes measured by the altimeter, an instrument that measures the altitude of the surface, are shown in meters on the left-hand axis. Also shown for comparison is the altitude of the highest terrestrial peak, Mt. Everest. You can see from the graph that Olympus Mons is much larger than Mt. Everest (and Mauna Loa, from the ocean floor up!). Olympus Mons is also wider than the entire chain of Hawaiian Islands.
If you return to the first page of this tour and look at the comparison of images of Earth and Mars, you'll remember that Mars is about one-third the size of Earth. Considering that, it's remarkable that such a large volcano could exist on Mars.