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oblate spheroid	oblate spheroid

A spheroid is a quadric surface obtained by rotating an ellipse about one of its principal axes; in other words, an ellipsoid with two equal semi-diameters.

If the ellipse is rotated about its major axis, the result is a prolate (elongated) spheroid, like a rugby ball. If the ellipse is rotated about its minor axis, the result is an oblate (flattened) spheroid, like a lentil. If the generating ellipse is a circle, the result is a sphere.

Because of its rotation, the Earth's shape is more like an oblate spheroid than a sphere. In cartography, in fact, the Earth is often assumed to be a standard oblate spheroid. In the current World Geodetic System model, the radius is approximately 6,378.137 km at the equator and 6,356.752 km at the poles (a difference of over 21 km).

Volume

The volume of a spheroid (of any kind) is 

In experimental biology, tumor growth is approximated to take the shape of a spheroid. Often, cancer studies involve the implantation of tumors subcutaneously in mice. Such studies require a simple mechanism by which to evaluate tumor burden. One such method is for two blinded researchers to measure tumor dimensions length and width with calipers. The depth is not measured. Tumor volume in cubic millimeters can be approximated with the following formula:

Volume = 0.52(Width^2)Length.