How big is the Moon?

Comparing the Size of the Moon and EarthEarth is about four times the size of the Moon
A tennis ball and a basketball are placed side by side on a blue background, illustrating their size difference. A label explains this is like comparing the Moon to Earth if Earth were a basketball and the Moon a tennis ball.
Comparing the Size of a Tennis Ball and a BasketballIf Earth were the size of a basketball, the Moon would be about the size of a tennis ball.

The Moon is a spherical rocky body with a mean equatorial radius of approximately 1,738 kilometers (1,080 miles) and a diameter of roughly 3,476 kilometers (2,160 miles). In terms of mass, the Moon is relatively massive for a natural satellite, with a mass ratio compared to Earth that is larger than that of most other natural satellites to their respective planets. Its size is substantial enough to exert a strong gravitational influence on Earth, affecting tides and even the length of our days; it is even strong enough that the Moon and Earth orbit a common barycenter located between the two bodies’ cores rather than the Moon orbiting Earth’s center.

The Editors of Encyclopaedia Britannica
Citation Information
Article Title: How big is the Moon?
Website Name: Encyclopaedia Britannica
Publisher: Encyclopaedia Britannica, Inc.
Date Published: 05 November 2026
Access Date: November 13, 2026