Shape and Size

1.1 - Know that the shape of the Earth is an oblate spheroid

1.2 - Be able to use information about the mean diameter of the Earth (13,000 km)

Earth is not a perfect sphere. It is an oblate spheroid. It’s flattened at the poles and bulges at the equator.
The Earth is 12,756km at the equator and 12,714km from pole to pole. We round this up to 13,000km.

The diagram on this page is an exaggeration - in reality the difference is very small.

It is thought this shape was caused by the rotation of the early molten Earth.

Early astronomers knew that Earth was round for several reasons:

  • The Moon is round.
  • The shadow of the Earth on the Moon during a lunar eclipse is round.
  • Travellers going north or south see different stars not visible from elsewhere.
  • Travellers recording shadows at different angles on the same date.
  • Tall ships appearing to 'sink' as they move over the horizon


km > Radius Diameter Circ*
Equator 6,378.1 12,756.3 40,075
Poles 6,356.8 12,715.4 40,008
Difference 21.3 40.9 67



Earth's diameter is approximately 13,000km wide


The Shape of the Earth Mathematical Imagery