Measured at the equator, Earth is 7,926 miles (12,756 kilometers) in diameter, or the distance through the center.
Measured from geographic pole to pole, Earth is 7,900 miles (12,714 kilometers) in diameter.
The measurements differ because Earth is not a true sphere.
The pressure of rotation makes Earth bulge slightly in the middle so that it is shaped more like a tangerine than a tennis ball. In circumference, or the distance around the middle, Earth is 24,902 miles (40,075 kilometers) at the equator.
Earth bulges slightly at the equator, it is not a perfect sphere.
This is because centrifugal force created by its rotation pushes out the material at Earth’s center.