Britannica
Sources used in this answer
How big is Mercury compared with Earth and the Moon?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
Mercury
Mercury as seen by the Messenger probe, January 14, 2008. This image shows half of the hemisphere missed by Mariner 10 in 1974–75 and was snapped by Messenger's Wide Angle Camera when it was about 27,000 km (17,000 miles) from the planet.
Mercury is the smallest major planet in the solar system. While it is often compared to the Moon due to their roughly similar size and cratered appearance, Mercury is significantly more massive and dense.123
In terms of physical dimensions, Mercury has a mean radius of approximately 2,440 km (1,516 miles). For comparison, Earth is substantially larger, with a mean radius of approximately 6,371 km. Mercury is so small that it is even smaller than some moons in the solar system, such as Ganymede and Titan.12
Despite its small size, Mercury possesses a high density, with a large metallic core that accounts for about 61 percent of its volume—a much higher proportion than the core of the Moon (4 percent) or Earth (16 percent).3