The average calculated width is 4 to 5 meters (13 to 16 feet). As the wall is very long and passes through different landforms, the nature of geographical locations through different sections varies. So the height and width of the wall also differ from section to section.
For an idea, the width can be estimated by the point that at least four horses can pass through the wall at a time. The width was set by keeping in mind access to soldiers and the base support of the wall. The base support was very necessary because the structure is too long to hold the whole wall together. Also, it was needed to construct it strong enough to bare different climatic conditions, along with earthquakes. The average calculated width of the base of the Great Wall of China is about 6.5 meters (21 feet). The design of the wider base and comparatively thin upper structure makes the wall more solid.
This design was very beneficial for the soldiers of that time to march and convey the supplies or weapons during wartime. The wall itself on the top usually measures an average of 0.4-0.5 meters (1.3-1.6 feet) thick.