Earth's rotation, internal density variations, and external tidal forces cause its shape to deviate systematically from a perfect sphere. Local See more

The Earth can be modeled as a sphere in many ways. This section describes the common ways. The various radii derived here use the notation … See more

Earth's diameter is simply twice Earth's radius; for example, equatorial diameter (2a) and polar diameter (2b). For the WGS84 ellipsoid, that's respectively:
• 2a … See more

The following radii are derived from the World Geodetic System 1984 (WGS-84) reference ellipsoid. It is an idealized surface, and the Earth measurements used to calculate it have an uncertainty of ±2 m in both the equatorial and polar dimensions. … See more

Geocentric radius
The geocentric radius is the distance from the Earth's center to a point on the spheroid surface at See more

The mathematical expressions above apply over the surface of the ellipsoid. The cases below considers Earth's topography, above or below a reference ellipsoid. As such, they are … See more

In astronomy, the International Astronomical Union denotes the nominal equatorial Earth radius as $${\displaystyle {\mathcal {R}}_{e\mathrm {E} }^{\mathrm {N} }}$$, … See more