Mercury is the smallest planet in our solar system with a diameter of about 3,030 to 3,032 miles (4,878 to 4,879 kilometers), which is a little more than one-third the size of Earth

. Its mean radius is approximately 1,516 miles (2,440 kilometers)

. To put it in perspective, if Earth were the size of a baseball, Mercury would be about the size of a golf ball

. Mercury's circumference at the equator is about 9,525 miles (15,329 kilometers)

. Mercury's size is comparable to the continental United States and it is just slightly larger than Earth's Moon

. Despite its small size, Mercury is very dense, second only to Earth, with a density of 5.427 grams per cubic centimeter