What Is the Size of Earth?

The Earth has a mean radius of 3,959 miles. Its equatorial diameter is just over twice that, at 7,926 miles. This figure is somewhat higher than double the mean radius, owing to the Earth's equatorial bulge, which pushes out the crust at low latitudes.

The oblate geometry of the Earth has interesting consequences. One result of the planet's equatorial bulge is that the circumference of the Earth at its equator is 24,902 miles, while the pole-to-pole, or meridional, circumference is only 24,860 miles, a difference of 42 miles. This difference is the reason the Earth is technically known as an oblate spheroid.