The Earth is the largest of the terrestrial planets in the Solar System, and the 3rd planet from the Sun. Are you looking for the circumference and diameter of the Earth?
The equatorial circumference of the Earth is 40,075 km. This is the distance around the equator of the Earth. If you measure the circumference of the Earth, while passing through the poles, the distance is only 40,007 km. This is because the Earth isn’t a perfect sphere. It’s rotating rapidly, which causes the equator to bulge out.
The equatorial diameter of the Earth is 12,756 km. This is the diameter of the Earth measured from one side of the Earth, passing through the center. If you go from pole to pole through the center, the distance is only 12,713 km.
We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.