Mercury is significantly smaller than Earth. Its diameter is about 4,879 kilometers (3,032 miles), which is roughly 38% (a little more than one-third) the diameter of Earth, whose diameter is about 12,756 kilometers (7,926 miles)

. In terms of radius, Mercury's radius is approximately 2,440 kilometers (1,516 miles), compared to Earth's radius of about 6,378 kilometers (3,963 miles)

. To visualize, if Earth were the size of a nickel or a baseball, Mercury would be about the size of a blueberry or a golf ball, respectively

. Volume-wise, about 18 Mercurys would fit inside Earth

. Despite its smaller size, Mercury is very dense-second only to Earth-due to its large metallic core, which makes up about 85% of its radius

. Its mass is only about 5.5% that of Earth

. In summary, Mercury is about one-third the size of Earth in diameter, much smaller in volume and mass, but nearly as dense due to its large iron core. This makes Mercury the smallest planet in the solar system and distinctly smaller than Earth.