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The Earth's radius (represented as R_🜨 or ${\displaystyle R_{E}}$) is the distance from the center of Earth to a point on or near its surface.

Earth is shaped like a slightly flattened ball (an oblate spheroid). Because it is not perfectly round, Earth's radius varies. At the Equator, Earth's radius (called the equatorial radius) measures about 6,378 km (3,963 miles). At the North and South Poles, the planet's radius (called the polar radius) is slightly shorter: around 6,357 km (3,950 miles). The global average has been estimated at 6,371 kilometres (3,959 mi).

Earth radius
Cross section of Earth's Interior
General information
Unit system	astronomy, geophysics
Unit of	distance
Symbol	R🜨 or ${\displaystyle R_{E}}$, ${\displaystyle {\mathcal {R}}_{\mathrm {eE} }^{\mathrm {N} }}$
Conversions
1 R🜨 in ...	... is equal to ...
SI base unit	6.3781×106 m[1]
Metric system	6,357 to 6,378 km
English units	3,950 to 3,963 mi

Earth's radius can also be defined and measured using the radius of curvature. This calculation considers land and sea topography. As a result, it can produce a different result than measurement of the equatorial or polar radiuses.

"Earth radius" is sometimes used as a unit of measurement in astronomy and geophysics. The International Astronomical Union recommends that "Earth radius" should equal the planet's equatorial radius.

1. ↑ Mamajek, E. E; Prsa, A; Torres, G; et al. (2015). "IAU 2015 Resolution B3 on Recommended Nominal Conversion Constants for Selected Solar and Planetary Properties". arXiv:1510.07674 [astro-ph.SR].