Earth is smoother than a professional billiard ball when scaled down to the same size.

Earth has a diameter of about 12,742 kilometers. Mount Everest is 8.8 kilometers high and the Mariana Trench is 11 kilometers deep. The total distance between the highest and lowest points is about 19.8 kilometers.This difference is only 0.15% of the planet's total size. If Earth were shrunk to the size of a 2.25-inch pool ball, this entire range would be only 0.088 millimeters tall. This is thinner than a single strand of human hair.The World Pool-Billiard Association requires balls to be very round and smooth. A pool ball can have small variations in its shape of up to 0.005 inches. Earth's surface variations at that scale are even smaller than what is allowed for these balls.Earth also has a slight bulge at the equator caused by its rotation. This bulge is about 42.7 kilometers wide. Even with this extra width, the planet still fits within the roundness standards used for professional pool equipment.This comparison shows that Earth is nearly a perfect sphere. Our mountains and oceans seem huge to us, but they are very small compared to the volume of the planet.