Earth radius
A globally-average value is usually believed to be  with a 0.3% variability (±10 km) for the following reasons. The International Union of Geodesy and Geophysics (IUGG) provides three reference values: the mean radius (R) of three radii measured at two equator points and a pole; the authalic radius, which is the radius of a sphere with the same surface area (R); and the volumetric radius, which is the radius of a sphere having the same volume as the ellipsoid (R). All three values are about .