Neptune is the fourth largest planet in our solar system, after Jupiter, Saturn, and Uranus. It has a diameter of about 49,244 kilometers (30,600 miles), which is about four times that of Earth. Neptune's mass is about 17.2 times that of Earth, making it the most massive planet in the solar system after Jupiter and Saturn. Neptune is also the densest planet in the solar system, with a density of about 1.64 grams per cubic centimeter, which is about 50% denser than Earth.