# Earth radius conversions

The Earth radius conversion selector on this page selects the length/distance measurement unit to convert to starting from Earth radius (RE). To make a conversion starting from a unit of length other than Earth radius, simply click on the "Reset" button.

## About Earth radius

The **Earth radius**, or the **radius of the earth**, is the distance from the center of the Earth to the surface.

The average radius of the Earth is approximately 6.371 × 10^{6} meters (Earth radius ≈ 6.371 × 10^{6} m), the base unit of length in the International System of Units (SI). The average Earth radius (RE) is also equal to about 6,371 kilometers (km) (an SI unit of length), or 3,440 nautical miles (nmi) (a nautical unit of length), or approximately 3,959 miles (mi) or 20,902,231 feet (ft), which are US customary / Imperial units of length.

Since the Earth is not perfectly spherical but rather an oblate spheroid, the Earth radius is greater at the equator than it is at the poles. The equatorial radius of the Earth (or semi-major axis) is about 6,378 km (3,963 miles or 3,444 nautical miles), while the polar radius of the Earth (or semi-minor axis) is about 6,357 km (3,950 miles or 3,432 nautical miles).

The Earth radius is a unit of distance used in astronomy and geology.

Symbol: RE

Plural: Earth radii