How big is Moon? | Scale of the Universe

The Moon is Earth's only natural satellite, and it is about 3,475 kilometers (2,159 miles) across. That is its mean diameter, a little more than a quarter of Earth's width. It is the fifth-largest moon in the Solar System.

Size

NASA gives the Moon's mean radius as 1,737.4 kilometers, which makes its mean diameter about 3,475 kilometers. The Moon is very nearly round. Its radius at the equator, 1,738.1 kilometers, is only about 2 kilometers more than its radius at the poles.

The surface is not smooth, though. Its highest and lowest points are about 13 kilometers (8 miles) apart in height. Under the surface, the crust is about 40 kilometers (25 miles) thick on the side facing Earth, and up to about 60 kilometers (37 miles) thick on the far side.

Size comparisons

If Earth were shrunk to the size of a basketball, the Moon would be about the size of a tennis ball, orbiting about 7 meters (24 feet) away.
The Moon's average distance from Earth is 384,400 kilometers (238,900 miles), room for about 30 Earths side by side.
Earth has about 49 times the Moon's volume.
Jupiter's moon Io is about 5% wider than the Moon, and Europa is about nine-tenths of the Moon's width.
About 82 marathons laid end to end would reach across the Moon.

Why the Moon can cover the Sun

The Sun is about 400 times as wide as the Moon. It is also roughly 400 times farther away, so the two look almost the same size in Earth's sky. That is why, during a total solar eclipse, the Moon can almost exactly cover the Sun.

The match is not exact. The Moon's distance from Earth varies between about 357,000 and 407,000 kilometers as it orbits. When it is far away, it looks too small to cover the whole Sun, and a ring of sunlight shows around it. This is called an annular eclipse.

The Moon is also slowly moving away from Earth, by about 3.8 centimeters (1.5 inches) a year. More than 600 million years from now, it will always look too small to cover the whole Sun.

How the Moon formed

Scientists think the Moon formed after a body about the size of Mars crashed into Earth several billion years ago. Debris from both collected in orbit and came together as the Moon. The new Moon was molten at first. Within about 100 million years, most of this global "magma ocean" had hardened, and lighter rocks floated up to form the crust.

As of 2026, the Moon is the only world beyond Earth that people have visited. Apollo astronauts brought back 382 kilograms (842 pounds) of lunar rock and soil, which scientists are still studying.