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, and chek in Cantonese, and is 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, and a jeung in Cantonese, and is traditionally written as "丈".

Etymology

The English term shaku^[1][2] derives from the Japanese word shaku (尺^?). Early citations indicate that it entered the English language early in the 18th century.^[1]

China

1 chi (shaku in China) =

SI units
0.3333 m	333.3 mm
US customary / Imperial units
1.094 ft	13.12 in

1 chek (shaku in Hong Kong) =

SI units
0.371475 m	371.475 mm
US customary / Imperial units
1.21875 ft	14.6250 in

1 chi (shaku in Taiwan) =

SI units
0.3030 m	303.0 mm
US customary / Imperial units
0.9942 ft	11.93 in

Modern values

In the People's Republic of China, the Chinese counterpart of the shaku, known as the chi in Mandarin (Chinese: 尺; pinyin: chǐ; Wade–Giles: chih), has been defined since 1984 as exactly 1/3 of a meter, i.e. 33¹⁄₃ cm (approximately 1.094 ft). However, in the Hong Kong SAR the corresponding unit, pronounced chek (Chinese: 尺; Jyutping: chek) in Cantonese and spelled as "chek" in Hong Kong, is defined as exactly 0.371475 m (exactly 14⁵⁄₈ in).^[3][4] 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 (30¹⁄₃ cm).

Historical values

The study of ancient rulers, the values of which were founded on the shaku, 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.^[5]

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.^[6]

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).^[7]

Japan

1 shaku (Japan) =

SI units
0.3030 m	303.0 mm
US customary / Imperial units
0.9942 ft	11.93 in

Since 1891,^[8] the Japanese shaku (尺, shaku^?) has been defined to equal 10/33 meters (approximately 30.3 cm, or 11.93 inches), or 3.3 shaku to the meter.^[9] 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.^[10]

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 whiskers) and the other shaku was referred to as kanejaku (metal shaku).^[9]

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.^[10]

The Shōsōin in Nara has ivory one-shaku rulers, the kōgebachiru-no-shaku (紅牙撥鏤尺^?).^[11][12]

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.^[13]

See also

• Chinese units of measurement
• Japanese units of measurement
• Taiwanese units of measurement
• Units of measurement

Notes

1. ^ ^{a b} Oxford English Dictionary, Volume XV page 148
2. ^ Webster's Third New International Dictionary of the English Language, 1986
3. ^ Government of Hong Kong, Weights and Measures Ordinance of 1997
4. ^ WEIGHTS AND MEASURES ORDER - SCHEDULE (Hong Kong Regulations)
5. ^ Shen, Kangshen; Crossley, John N.; Lun, Anthony Wah-Cheung; Liu, Hui (1999). The nine chapters on the mathematical art: companion and commentary. Oxford University Press. p. 8. ISBN 0198539363. http://books.google.com.au/books?id=eiTJHRGTG6YC. 
6. ^ Liu, C. Y, A Research on the Implication of Zhang-Chi in Ancient Chinese Astronomical Records. ACTA ASTRONOMICA SINICA V.28:4, P. 402, 1987
7. ^ Carrington, Robert C. (1864). Foreign measures and their English values. Potter. p. 22. http://books.google.com.au/books?id=fIgBAAAAQAAJ. 
8. ^ Japanese Metric Changeover by Joseph B. Reid, President Emeritus, Canadian Metric Association (U.S. Metric Association page)
9. ^ ^{a b} Details of the two shaku units at sizes.com
10. ^ ^{a b} Heino Engel (1985). Measure and construction of the Japanese house. Tuttle Publishing. p. 22. ISBN 9780804814928. http://books.google.com.au/books?id=JqiLJD35FTUC. 
11. ^ 甲
12. ^ 乙
13. ^ A note on shakuhachi lengths

References

• Weiner, E S C;; Simpson, J A (1989, 2004). The Oxford English Dictionary. Oxford University Press. ISBN 0-19-861227-3.