Li (unit)

The li 里 was a unit of length and area used in China from the Qin period to the early Qing period, or from about the 3rd century BCE to the 18th century CE. The distance that it designated changed over time, but often it represented about one-half kilometer or one-third mile. When used as a measure of area, it designated the area of a square one li of distance on each side.

Until about 1000 CE, the li was defined as one-tenth of the distance a person could walk on level ground in two hours. In the Song era and for most of the time thereafter, it was officially set at 360 bu 步, but the length of the bu itself changed over time; it was supposed to represent a "double pace," or somewhat less than two meters.

During the Mongol Yuan dynasty (1279-1368), however, the li was officially defined as 240 bu, or two-thirds of the distance it represented before and after that period (i.e., about 380m or just over one-quarter mile).

Although China today uses the metric system, the word "li" still has cultural resonance, much as terms such as "inch" and "mile" are recognized in proverbs and historical texts by many people in English-speaking countries that have converted to metric. For instance, the Great Wall of China is called, in Chinese, "The Long Wall of 10,000 Li."