The Earth's mean radius is determined as the average distance from the physical center to the surface, based on a large number of samples. The value, symbolized rearth, is equal to approximately 6,371,000 meters (6.371 x 106 m). This is roughly 6,371 kilometers (km) or 3,960 statute miles.
The Earth is slightly oblate, so its radius in the plane of the equator is a little larger than its radius along the rotational axis. In addition, there are irregularities in the surface because of hills, mountains, tides, and rainfall.
Based on the value of rearth given here, the volume of the planet (Vearth), in meters cubed (m3), can be found using the standard formula for the volume V of a sphere in terms of its radius r:
V = (4/3)(pi) r3
Vearth = 1.083 x 1021 m3
Also see Table of Physical Units and Constants.