How Big Is Neptune? indicates that Neptune's diameter of 15,299 miles is fourth longest among the planets. At 102 trillion trillion kilograms, Neptune has the third-highest mass of the eight planets in the solar system. However, it was one of the last planets discovered because it is the farthest from the sun.

Cool Cosmos notes that Neptune's volume is 57.7 times that of Earth. Neptune has a large surface area of 2.9 billion square miles, though it consists of water and ice rather than solid ground. Because of its gas atmosphere and liquid surface, Neptune has a modest density of 1.638 grams per cubic centimeter.