Earth radius

Earth radius(represented asR_🜨or$R_{E}$) is the distance from the center ofEarthto a point on or near its surface. Approximating thefigure of Earthby anEarth spheroid,the radius ranges from a maximum of nearly 6,378 km (3,963 mi) (equatorial radius,representeda) to a minimum of nearly 6,357 km (3,950 mi) (polar radius,representedb).

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

Earth radius is sometimes used as aunit of measurementinastronomyandgeophysics.TheInternational Astronomical Unionrecommends that the radius at the equator should be used.

A globally-average value is usually believed to be 6,371 kilometres (3,959 mi) with a 0.3% variability (±10 km) for the following reasons. TheInternational Union of Geodesy and Geophysics(IUGG) provides three reference values: themean radius(R₁) of three radii measured at two equator points and a pole; theauthalic radius,which is the radius of a sphere with the same surface area (R₂); and thevolumetric radius,which is the radius of aspherehaving the same volume as theellipsoid(R₃). All three values are about 6,371 kilometres (3,959 mi).

Other ways to define and measure the Earth radius involve theradius of curvature.A few definitions yield values outside the range betweenpolarradius andequatorialradius because they include local orgeoidaltopographyor because they depend on abstract geometrical that are carefully thought about.