What is the shape of Earth commonly described as?

Earth is commonly described as an oblate spheroid: almost spherical, but slightly flattened at the poles and bulging at the equator.

The equatorial bulge is mainly a consequence of Earth’s rotation. Rotation produces centrifugal effects that push mass outward most strongly around the equator. Gravity still dominates, so Earth remains very close to a sphere, but its equatorial radius is larger than its polar radius.

In geodesy, scientists use reference ellipsoids to approximate Earth’s shape for mapping, surveying, navigation, and satellite positioning. The WGS 84 ellipsoid, used by GPS, models this flattening mathematically. The difference from a perfect sphere is small—roughly one part in 300—but it matters for precise measurements.

“Ellipsoid” is a broader geometric term, while “oblate spheroid” identifies the specific flattened form that best approximates Earth. Earth is not a perfect sphere, and its true physical surface is even more irregular because mountains, ocean trenches, tides, and variations in gravity create a shape called the geoid.