Planets - Calculate Diameter

Calculator for the diameters of Sun, Moon, Earth and the planets in kilometers, miles and compared to each other. Celestial bodies, especially fast rotating gas giants and stars, are bodies of revolution, which are thicker in the rotaion plane than in the polar cross section (so-called oblate spheroids). Therefore, three different kind of diameters can be choosen here. The equatorial diameter, extending from a point on the equator through the planet's center to the exactly opposite point, is hereby the largest diameter. The polar diameter, extending from the North Pole through the center to the South Pole, is the smallest. The average is not the arithmetic mean of these two values ​​but lies closer to the equatorial diameter.

Diameter: equatorial polar average

Kilometers:
Miles:
Diameters		km mile Earth diameter Jupiter diameter Sun diameter
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 diameter, then enter one value. The other values will be calculated.

Example: Saturn has about nine times Earth's diameter, slightly more for the equatorial, slighly less for the polar diameter.

A planet's mass is determined by its medium density and its diameter, whereas its surface area depends solely on its diameter, provided the precise shape of the spheroid is disregarded. This is a valid assumption, as rocky planets like Earth are nearly spherical. A planet's mass and diameter determine the strength of gravity at its surface. Surface area increases with the square of the diameter. Thus, a planet with twice the diameter has four times the surface area, one with three times the diameter has nine times the surface area, and so on. If the diameter is increased by a factor of 1.4142 (more specific √2), the surface area doubles. The diameter is twice the radius. Whether the radius or the diameter of a planet is cited depends on the context.

Last updated on 07/28/2026. Author: Jürgen Kummer

Calculators for Planets and Astronomy

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