Planets - Calculate Radius

Calculator for the radiuses of Sun, Moon, Earth and the planets in kilometers, miles and compared to each other. Radius is half the diameter, it quantifies the distance from the center to the edge of the celectial body. The planetary radius is important e.g. for the calculation of the gravitational acceleration.

Radius: equatorial polar average

Kilometers:
Miles:
Radiuses		km mile Earth radius Jupiter radius Sun radius
Moon:
Mercury:
Venus:
Earth:
Mars:
Jupiter:
Saturn:
Uranus:
Neptune:
Pluto:
Sun:

Round to   0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15   decimal places.

Please enter first the kind of radius, then enter one value. The other values will be calculated.

Example: Jupiter has about eleven times Earth's radius, slightly more for the equatorial, slighly less for the polar radius.

The equatorial radius is the distance from the center of a celestial body to a point on its equator. Correspondingly, the polar radius is the distance from the center to one of its two poles. Which specific point on the equator or which pole is chosen does not matter if the celestial body is an oblate spheroid. This shape is determined by two competing forces. One is gravity, which tends to pull the mass as close to the center as possible, resulting in a sphere. Once a body reaches a radius of 200 to 450 kilometers (depending on its composition), gravity ensures it takes on a roughly spherical shape. The second shaping force is centrifugal force, caused by the body's rotation around its polar axis, which tends to flatten it into a disk. The faster the rotation and the more malleable the body's material, the more the sphere is stretched outward at the sides, resulting in a more flattened spheroid. Consequently, the equatorial radius is at least as large as the polar radius, usually larger, though for rocky planets like Earth, the difference is slight. In contrast, the gas giant Jupiter is significantly more flattened because gas is much more easily deformed. The average radius lies closer to the equatorial radius than to the polar radius.
Whether the radius or the diameter is used for calculations depends on the context. The radius is more common in geometric contexts, such as when describing relationships within a system. However, when considering factors like apparent size, the diameter is often the more useful figure.

Last updated on 07/29/2026. Author: Jürgen Kummer

Calculators for Planets and Astronomy

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