The diameter of Uranus is 51,118 km. Just for comparison, this about 4 times bigger than the diameter of the Earth, at 12,742 km across.
Things get a little more complicated, however. Here’s the thing. As you probably know, Uranus is spinning on its axis, completing a day in just over 17 hours. The rapidly spin of Uranus causes it to flatten out slightly. In other words, the diameter from pole to pole is slightly less than the diameter across the equator. The diameter of Uranus from pole to pole is 49,946. If you subtract the two, you’ll find that the polar diameter is 1,172 km less than the equatorial diameter.
Want more diameters? Here’s the diameter of Earth, the diameter of the Sun, and the diameter of Jupiter, the largest planet in the Solar System.
We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.