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How much larger is Earth’s equatorial radius than its polar radius?

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Diagram showing the deflection of the vertical from the geoid to the ellipsoid or spheroid, with labeled lines for geoid, spheroid, rock surface, ocean, and geoid height in a geology context. — geoid Deflection of the vertical from the geoid to the spheroid.

Earth’s equatorial radius is approximately 21 kilometres (13 miles) larger than its polar radius.12

More specifically, based on planetary data, the equatorial radius is 6,378.14 km, while the polar radius is 6,356.78 km. This difference occurs because Earth is an oblate spheroid—a shape resulting from the centrifugal force generated by the planet's rotation, which causes it to bulge at the Equator. In geodesy, this shape is often represented by a reference ellipsoid to simplify calculations regarding the planet's size and shape.3412