Chi (unit)

Chi (China)
Wooden ruler of the western Han dynasty, unearthed at Jinguan Pass Site in Jinta County
Unit system	traditional Chinese unit
Unit of	length
1 chi (china) in ...	... is equal to ...
metric (SI) units	1/3 m  ~333.3 mm
imperial/US units	~1.0936 ft  ~13.123 in

Chek (Hong Kong)
a section of an old Hong Kong ruler, showing the last (10th) cun of a chi. One can see that the chi in that jurisdiction was exactly equal to 14 5/8 of an inch. A metric ruler is shown next to it for comparison
Unit system	traditional Chinese unit
Unit of	length
1 chek (hong kong) in ...	... is equal to ...
metric (SI) units	6999371475000000000♠0.371475 m  ~371.5 mm
imperial/US units	1.21875 ft  14 5/8 in

The chi is a traditional Chinese unit of length. Although it is often translated as the "Chinese foot", its length was originally derived from the distance measured by a human hand, from the tip of the thumb to the tip of the forefinger similar to the ancient Span. It first appeared during China's Shang dynasty approximately 3000 years ago and has since been adopted by other East Asian cultures such as Japan, Korea, and Vietnam. Its present value is standardized around a third of a meter, although the exact standards vary among the mainland of the People's Republic of China, its special administrative region of Hong Kong, and Taiwan.

In its ancient and modern forms, the chi is divided into 10 smaller units known as cun (the "Chinese inch") and 10 chi together form one zhang.

In the People's Republic of China chi has been defined since 1984 as exactly 1/3 of a meter, i.e., 33 ¹⁄₃ cm (approximately 1.094 ft). However, in the Hong Kong SAR the corresponding unit, pronounced chek in Cantonese, is defined as exactly 0.371475 m (exactly  14 ⁵⁄₈ in). The two units are sometimes referred to in English as "Chinese foot" and "Hong Kong foot".