How long is the Great Wall of China according to official measurements?

According to official measurements, the Great Wall of China is about 21,196 kilometres long.

This figure includes many sections from different historical periods, along with trenches and natural barriers incorporated into the defensive system. It is therefore much larger than the length of the best-preserved Ming-era wall alone.

Construction and rebuilding took place over more than 2,000 years. Early states built defensive walls before China was unified, while the Ming dynasty later constructed or strengthened many of the brick and stone sections commonly visited today.

The Great Wall was not one continuous wall built at one time, and it did not reliably stop every invasion. It served multiple purposes, including defense, border control, signaling, and regulating movement and trade. The popular claim that it is visible from the Moon is false.