The shape of Earth most closely resembles an oblate spheroid. An oblate spheroid is a three-dimensional shape that is slightly flattened at the poles and bulges at the equator. This shape is caused by the rotation of Earth on its axis, which creates a centrifugal force that pushes material away from the poles and towards the equator. The equatorial radius of Earth is approximately 6,378 kilometers, while the polar radius is approximately 6,357 kilometers. This means that Earth is about 43 kilometers wider at the equator than it is at the poles.