Shaku (unit)

The shaku (尺) is a traditional unit of measure used throughout Asia with a length approximately equal to a foot. It is variously called shaku in Japanese, chi in Mandarin, chek in Cantonese, and written as "呎" in Hong Kong. As with other measurements, it was originally derived from nature: the average length between nodes on bamboo. The actual length varies slightly by country.

The shaku may be divided into ten smaller units (寸), known as either cun in Mandarin, sun in Japanese, or tsun in Cantonese. Ten shaku are equal to a jō in Japanese, a zhang in Mandarin, a jeung in Cantonese, and written as "丈" traditionally.

Etymology
The English term shaku derives from the Japanese word shaku (尺). Early citations indicate that it entered the English language early in the 18th century.

Modern values
In the People's Republic of China, the Chinese counterpart of the shaku, known as the chi in Mandarin, 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 and spelled as "chek" in Hong Kong, 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".

Usage of shaku in In Taiwan is the same as the Japanese shaku, i.e. 10/33 of meter (30 1/3 cm).

Historical values
The study of ancient rulers and other artifacts whose size in the contemporary shaku was known allowed modern researchers to surmise that during the 2nd century BC to 3rd century AD the (Qin Dynasty to Kingdoms of Wu and Wei), the value of the shaku varied between 23.1 to 24.3 cm.

It is thought that the ancient Chinese astronomers also used shaku 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 shaku, depending on the part of the country and the application, varied between 31 and 36 cm. According to an 1864 British report, in most of China the shaku used by engineers in public works was equal to 12.71 English inch (32.28 cm), the surveyors' shaku was 12.058 inch (30.62 cm), while the value generally used for measuring distances was 12.17 inch (30.91 cm). In Guangzhou, however, the shaku used for local trade varied from 14.625 to 14.81 inch (37.15-37.62 cm) - i.e., very close to the modern shaku; the value fixed by a Sino-British treaty for the purposes of customs duties in Hong Kong was 14.1 inch (35.81 cm).

Japan
Since 1891, the Japanese shaku (尺) has been defined to equal 10/33 meters (approximately 30.3 cm, or 11.93 inches), or 3.3 shaku to the meter. A single shaku is divided into 10 sun.

In the past, a longer value of shaku (known as kōrai-shaku), equal to approximately 1.17 of modern standard shaku, or 35.5 cm (14 inches) was in use.

Another unit of length also called the shaku was used only for measuring cloth. This shaku measured 125/330 meters (approximately 37.9 cm, or 14.9 inches). When a distinction needed to be made between the two shaku, the cloth unit was referred to as kujirajaku (whale shaku, as the rulers for measuring cloth were made from whale whisker) and the other shaku was referred to as kanejaku (metal shaku).

While Japanese law required official use of these units be discontinued on March 31, 1966, the shaku is still used in some fields in Japan, such as traditional carpentry. The ken and jō are larger than a shaku: six shaku make up one ken; ten shaku make up one jō. The ken is commonly the distance between pillars in traditional buildings such as Buddhist temples and Shinto shrines.

The Shōsōin in Nara has ivory one-shaku rulers, the kōgebachiru-no-shaku (紅牙撥鏤尺).

The shakuhachi is a Japanese bamboo flute whose name (尺八) means "[one] shaku eight [sun]", because traditionally its standard length was one shaku and eight sun, i.e. 1.8 shaku