Earth - mean spherical radius (NM)

The Earth's Mean Spherical Radius (NM) is 3440.2753 nmi.

Derivation

The mean radius equation computes the mean radius of an ellipsoid             Ellipsoid with semi-axes of lengths  a and b.

Since the Earth is an oblate spheroid, closely approximated by an ellipsoid, the IUGG defines the Earth's mean radius using:

• a =  Equatorial radius (6,378.1370 km)
• b =  Polar radius (6,356.7523 km)

This computes and Earth mean radius of 6,371.009 kilometers (3,958.761 mi).