How big is Uranus?

Uranus is the seventh planet from the Sun, and it is 50,724 kilometers (31,518 miles) across on average. That figure is its mean diameter, the width of a perfect sphere with the same volume as Uranus. Only Jupiter and Saturn are wider. Uranus is an ice giant, made mostly of a hot, dense fluid of water, methane and ammonia, and it spins tipped over on its side.

Size

Uranus has no solid surface, so its size is measured to a level in its atmosphere. Astronomers use the height where the pressure is 1 bar, about the same as the air pressure at sea level on Earth.

Measured that way, Uranus is 51,118 kilometers (31,763 miles) wide at its equator and 49,946 kilometers (31,035 miles) from pole to pole, so it is slightly flattened. Its mean diameter is known to within about 15 kilometers.

Size comparisons

Uranus is about four times as wide as Earth, and its volume is about 63 times Earth's.
Neptune is 49,244 kilometers (30,599 miles) across on average, so Uranus is about 1,480 kilometers (920 miles) wider. Neptune has about 18% more mass, though.
Saturn is 116,464 kilometers (72,367 miles) across on average, about 2.3 times as wide as Uranus.
If Earth were shrunk to the size of a basketball 24 centimeters (9.4 inches) across, Uranus would be a ball about 96 centimeters (3.1 feet) across.

A planet on its side

Uranus is the only planet whose equator is nearly at a right angle to its path around the Sun: it is tilted by 97.77 degrees. As a result, it seems to roll around the Sun like a ball. The tilt may be the result of a collision with an object the size of Earth long ago.

A year on Uranus lasts about 84 Earth years. Because of the tilt, the Sun shines directly over each pole for nearly a quarter of that time, while the other half of the planet has a dark winter 21 years long. Uranus and Venus are the only planets that spin in the opposite direction from the others.

Discovery and exploration

Uranus was the first planet found with the help of a telescope. The astronomer William Herschel discovered it on March 13, 1781, although he first thought it was a comet or a star. It is named after Uranus, the Greek god of the sky. Only one spacecraft has visited Uranus: NASA's Voyager 2, which flew past on January 24, 1986.