The Moon is by size and mass the fifth largest natural satellite of the Solar System, categorizeable as one of its planetary-mass moons, making it a satellite planet under the geophysical definitions of the term.[17] It is smaller than Mercury and considerably larger than the largest dwarf planet of the Solar System, Pluto. While the minor-planet moon Charon of the Pluto-Charon system is larger relative to Pluto,[g][59] the Moon is the largest natural satellite of the Solar System relative to their primary planets.[h]
The Moon's diameter is about 3,500 km, more than a quarter of Earth's, with the face of the Moon comparable to the width of Australia.[16] The whole surface area of the Moon is about 38 million square kilometers, slightly less than the area of the Americas (North and South America).
The Moon's mass is 1/81 of Earth's,[60] being the second densest among the planetary moons, and having the second highest surface gravity, after Io, at 0.1654 g and an escape velocity of 2.38 km/s (8600 km/h; 5300 mph).