Chi (unit)

The chi is a traditional Chinese unit of length. Although it is often translated as the "", 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, and is 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 ("shaku"), Korea ("ja/cheok"), and Vietnam ("thước"). Its present value is standardized at around , 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"). 10 chi are equal to 1 zhàng.
Modern values.
In the People's Republic of China "chi" has been defined since 1984 as exactly 1/3 of a metre, i.e., . However, in the Hong Kong SAR the corresponding unit, pronounced "chek" in Cantonese, is defined as exactly .
The two units are sometimes referred to in English as "Chinese foot" and "Hong Kong foot".
In Taiwan, "chi" is the same as the Japanese "shaku", i.e., .
Historical values.
The study of ancient rulers and other artifacts whose size in the contemporary "chi" was known allowed modern researchers to surmise that during the 2nd century BC to 3rd century AD the (Qin Dynasty to Han Dynasty to the Three Kingdoms period), the value of the "chi" varied between . Even earlier, during the Warring States era, the value of "chi" was essentially the same.
It is thought that the ancient Chinese astronomers also used "chi" as an angular unit; modern analysis of historical records indicates that it may have been equal to one degree.
In the 19th century, the value of the "chi", depending on the part of the country and the application, varied between . According to an 1864 British report, in most of China the "chi" used by engineers in public works was equal to , the surveyors' "chi" was , while the value generally used for measuring distances was . In Guangzhou, however, the "chi" used for local trade varied from – i.e., very close to the modern "chek". The value fixed by a Sino-British treaty for the purposes of customs duties in Hong Kong was .
Usage in Chinese language.
Due to its long history and its widespread usage, "chi" (along with "cun") has also seen metaphorical usages in the Chinese language. For example, "chi cun" (), a word made up of the units "chi" and "cun", refers to the dimensions of an object, while the idiom "dé cùn jìn chǐ" () means "extremely greedy".
In informal use in China, "chi" is also sometimes used to refer to the US or imperial foot.