Earth is the fifth largest of the planets in the solar system — smaller than the four gas giants,Jupiter, Saturn, UranusandNeptune, but larger than the three other rocky planets, Mercury, Marsand Venus.

Earth has a diameter of roughly 8,000 miles (13,000 kilometers), and is round because gravity pulls matter into a ball, although it is not perfectly round, instead being more of an "oblate spheroid" whose spin causes it to be squashed at its poles and swollen at the equator.