Chinese people often call the Great Wall "the 5,000-Kilometer-Long Wall" ("3,100-Mile-Long Wall"). However, it's hard to give it an accurate length, as some of the sections have eroded away completely or have been developed over with roads, villages, etc.

Popular Chinese: "the 5,000-Km-Long Wall" (万里长城 Wàn-Lǐ Chángchéng /wann-lee channg-chnng/ 'Ten-Thousand-Li Great Wall' see below)

The Official Length: 21,196 km (13,170 mi)

After a five-year-long survey, the total length of the Great Wall was measured. On June 5th, 2012, the State Administration of Cultural Heritage announced that the official length of the Great Wall is 21,196.18 km (13,170.7 mi). This is the first time that China has scientifically and systematically measured the length of the Great Wall.

jinshanlingA watchtower relic at Jinshanling

It's a misleading figure as some sections of different eras were built on top of or right next to each other. Also isolated sections of fortified wall defending state boundaries are included, not just China's northern border wall(s) that people generally think the Great Wall to be.

All Known Sections of the "Great Wall" Were Measured

The Great Wall measured covers all the sections built by seven Warring States (475–221 BC) and at least seven dynasties from Qin to Ming (221 BC – 1644 AD) in 15 provincial-level areas: Beijing, Tianjin, Liaoning, Jilin, Heilongjiang, Hebei, Henan, Shandong, Shanxi, Shaanxi, Hubei, Inner Mongolia, Ningxia, Gansu, and Qinghai. The measured length includes 43,721 relics: walls, trenches, towers, walled fortresses, etc.

The Ming Great Wall's Length: 8,851 km (5,500 mi)

Most of the Great Wall visited and seen on photos was built in the Ming Dynasty.

On June 5th, 2012, the State Administration of Cultural Heritage and National Administration of Surveying and Mapping announced on April 18th, 2009 that the Great Wall of the Ming Dynasty: (1368 – 1644) was 8851.8 km long.

What Was Actually Measured

They measured Great Wall sections in 10 provinces: Liaoning, Hebei, Tianjin, Beijing, Shanxi, Inner Mongolia, Shaanxi, Ningxia, Gansu, and Qinghai.

They included in the length trenches and natural barriers like mountains, rivers, and lakes. Estimates of the length of actual wall come to over 6,200 km (3,900 miles). However, this includes many side branches that don't contribute to the west-to-east “length”.

The shortest distance from the most westerly point of the Ming Great Wall ('The First Strategic Post of the Great Wall' in Jiayuguan) to its most easterly point (Hushan on the Korean border) is 2,235 km (1,389 mi).

Why Chinese Call It the ‘5,000-Km-Long Wall’

The Great Wall has been called "Wan-Li Changcheng" since the Qin Dynasty (221–206 BC).

Wan means 10,000, and a li is half a kilometer. So 10,000 li is 5,000 km (3,100 miles), which was a actually a good estimation of the Great Wall length in the Qin Dynasty. However it continued in use through future dynasties, despite the Great Wall becoming longer.

Wan is also popularly used to mean 'a great number' in Chinese. So, a better translation of Wan-Li Changcheng would probably be "the Great-Number-of-Li-Long Wall", or "the Great Wall" for short!

Source: chinahighlights.com