what is neptune size relative to earth (diameter-miles/km)
Neptune is the 4th largest planet in the Solar System, after Jupiter, Saturn, and Uranus. Itâs much larger than the terrestrial planets: Mercury, Venus, Earth and Mars. The diameter of Neptune is 49,500 km. Need some comparison? Thatâs approximately 3.9 times the diameter of Earth. In other words, you could put almost 4 Earths side to side to match the diameter of Neptune. The volume of Neptune is 6.25 x 10 13 km 3.