The largest terrestrial, or rocky, planet in our Solar System is Earth. Terrestrial planets are characterized by their solid, rocky surfaces and are distinct from gas giants. Earth has a diameter of about 12,742 kilometers (7,918 miles), making it the largest among the four terrestrial planets, which include Mercury, Venus, Earth, and Mars. Earth not only has the greatest diameter but also the highest mass and volume. Its size can be attributed to its gravitational effect, which has allowed it to retain a significant atmosphere and support a diverse range of geological and biological activities.