Shaku (a unit of length defined by the traditional East Asian system of weights and measures) ()

Shaku (尺) is one of the units in the traditional East Asian system of weights and measures. This system of measurement is widely used in East Asia. In Japan, 1 shaku was set 10 over 33 meters (about 30.3 centimeters). In China, 1 shaku was set 1 over 3 meters (about 33.3 centimeters). Additionally, the Chinese character 尺 (shaku) was also used to represent a meter. For distinction, the former is called shi-chi and the latter gong-chi (refer to the article of Shizhi [Chinese units system of measurement]).

The term "Shakkotsu" (the Ulna bone), a bone of a forearm in human body, is derived from its length as it is often around this shaku.

It is a standard unit of length in the traditional system of weights and measures, and by extension, also the length of object or measuring ruler. The length of a movie film and its edited sequence are called 'shaku' because of previously-mentioned reason. By further extension, it became to refer the time allotted in programs of TV or radio, various events, and so on.


Studies indicate that the unit of shaku already existed during the period of Shang Dynasty in the ancient China. The Chinese character '尺' (shaku) was derived from the shape of spreading thumb and index finger. The shaku was originally an anthropomorphic unit that 1 shaku was defined as the length between the tips of thumb and middle finger of open hand. This length is usually about 18 centimeters, which is about 60 percents of today's 1 shaku.

Because the anthropomorphic unit was varied in its length depending on the user, an official shaku unit was defined by a particular length for 1 shaku later years. However, this official shaku unit gradually grew longer in more recent years. The private shaku unit became gradually longer which the government of the time had to confirm, and the official shaku unit was redefine. There is also a study that longer the official shaku unit became, more tax revenue based on the shaku, the length of a product (a roll of a fabric, and so on) became. Around B.C. 1000 during Zhou Dynasty, 1 shaku was extended, about 24 centimeters. The other units in the traditional East Asian system of weights and measures were also redefined according to the shaku.

However, aside from the private and the official shaku, the shaku used particularly by carpenters did not change much for a long time. The shaku unit used by carpenters is called kane-jaku (also known as kyoku-jaku). While kane-jaku is originally the carpenter's square scale used by carpenters, it became to refer the shaku unit marked with the scale. It is considered today that this kane-jaku unit did not change because the construction and architectural techniques were handed down from masters to pupils outside of political influences. The official shaku unit was defined for the collection of tax or business transactions, and that did not concern with the shaku unit used among artisans. The kane-jaku was derived from bu (歩; one of the traditional system of weights and measures) used for measuring the area of a land space. Originally 1 bu unit was defined by the length of two steps, and 1 bu square was the 1 bu of area. 1 shaku of the kane-jaku was defined as a half of the bu. In other words, 1 shaku of the kane-jaku was the length of one step (the area of 1 bu became larger to be 6 shaku square in the kane-jaku for present 1 bu). The fact 1 shaku of the kane-jaku was quite close to the unit of feet used in the Western countries was not by chance because both units were based on the length defined by the measurement of a foot.

During Sui Dynasty, new units da-chi (a large shaku) and xiao-chi (a small shaku) based on the kane-jaku were enacted as official shaku units which the government of Tang succeeded as well. These units were introduced in Japan, and o-shaku (a large shaku) and sho-shaku (a small shaku) were enacted in the Taiho Ritsuryo (the Code of Taiho) established in 701. There is also another study that since koma-jaku, which was introduced from the Kingdom of Goryeo and 2 shaku larger than the da-chi, was spread before the Taiho Ritsuryo in Japan; the da-chi of Tang became sho-shaku. In this study, gofuku-jaku (a shaku unit used for producing cloth), which was equivalent to 1 shaku 2 sun of the later kane-jaku, was considered to be derived from the koma-jaku. Furthermore, Hiroshi ARAI says the kokan-jaku (ancient Korean shaku) theory from the analysis of actual measurements of temples and others that 0.268-meter shaku was used, not the koma-jaku. In any case, sho-shaku later became out of use, and o-shaku became the official shaku unit in Japan. The da-chi used in Tang Dynasty was equivalent to 9.78 sun (29.63 centimeters) in today's kane-jaku, which suggests that the unit length has not changed much since then.

The official shaku unit was not maintained after the collapse of the Ritsuryo system, and various kind of shaku units were used throughout Japan. The representative shaku units were take-jaku (bamboo shaku; also known as kyoho-jaku [shaku of Kyoho era]) used in Kyoto region and tetsu-jaku (metal shaku; also known as matashiro-shaku [a carpenter's scale made by a joiner Matashiro]) used in Osaka region. Tetsu-jaku was about 1.4 times of the take-jaku. A scholar, Tadataka INO introduced setchu-jaku (averaged shaku) by averaging and integrating the tetsu-jaku and the take-jaku. In Meiji period, the government adopted the setchu-jaku as the official kane-jaku which was defined that 1 shaku was equivalent to 10 over 33 of the meter standard (that is, 10 over 33 meters). Generally, 'shaku' simply means the kane-jaku in Japan.

By the new weights and measures system established in 1958, the traditional system of weights and measures was eliminated as official units and prohibited to use in business purposes after that.

In China, the xiao-chi was not used after Tang Dynasty period, while the da-chi was used and gradually elongated to 36 centimeters by the end of Qing Dynasty. Based on the meter, the da-chi was officially defined as a third meter (about 33.3 centimeters) in 1929.

The Kujira-jaku

Other than the kane-jaku, various type of shaku was invented for particular usages. For example, kujira-jaku (literally, whale shaku) and gofuku-jaku (literally, kimono [Japanese traditional cloth] shaku) and others were used among tailors of kimono. Today's kujira-jaku was equivalent of 1 shaku 2 sun 5 bu (分; 1 bu is a 10th sun) in the kane-jaku. The gofuku-jaku was equivalent of 1 shaku and 2 sun in the kane-jaku. The origins of the kujira-jaku and the gofuku-jaku have not been specified yet. Some say that the kujira-jaku could have been derived from koma-jaku (Goryeo shaku) used before the Taiho Ritsuryo code, and other say that the kujira-jaku was invented in the Muromachi period. Since 1 koma-jaku was equivalent of 1.1736 shaku in the present kane-jaku, a theory suggests the koma-jaku is the origin of the gofuku-jaku, rather than the kujira-jaku. Other than the kane-jaku, Meiji government allowed the kujira-jaku as the limited use for the measurement unit of a clothing fabric, while other shaku including the gofuku-jaku were abolished. The shaku of the kujira-jaku (kujira-jaku shaku) was defined as 25 over 66 meters (about 37.88 centimeters).

There is a kobanashi (funny story) in early Edo period that Great Buddha statue of Nara and kujira (whale) of Tosa Province argued who was bigger; in the end, 'the kujira, for the kujira-jaku, was 2 sun longer than the kane, for the kane-jaku' (kane are the generic terms of metals, thus it means the Great Buddha statue in this case). The name 'kujira-jaku' was derived from the fact that the ruler used for tailoring cloth was made of flexible baleen.

Various kind of Shaku Measures

O-shaku in the Taiho Ritsuryo

About 35.6 centimeters.

Derived from the koma-jaku. Used for measuring the dimension of a territory, and so on.

Sho-shaku in the Taiho Ritsuryo

About 29.6 centimeters (1 shaku and 2 sun in the sho-shaku was equivalent to 1 shaku in the o-shaku)

Derived from the kara-jaku (shaku unit used in Tang Dynasty of China). Used commonly after Heian period.

The Tetsu-jaku (the Matashiro-jaku)

About 30.258 centimeters.

It is said to be invented by a sashimonoshi (cabinetmaker) Matashiro in Kyoto during Eisho era (1504 to 1520) and was mainly used among carpenters.

The Take-jaku (the Kyoho-jaku)

About 30.363 centimeters.

Yoshimune TOKUGAWA copied an ancient shaku unit handed down in Kumano jinja-Shrine of Kishu Domain to use for astronomical observation.

The Setchu-jaku

About 30.304 centimeters.

Invented by Tadataka INO by averaging and integrating the matashiro-jaku and the kyoho-jaku for land survey. It became the basis of the kane-jaku under the measurement regulation established in Meiji period.

The Kujira-jaku

About 37.88 centimeters (1 shaku 2 sun 5 nu in the kane-jaku)

Defined as 25 over 66 meters in the Meiji measurement regulation.

Mainly used for the measurement related with kimono. The length of the kujira-jaku are used in 6 shaku fundoshi (Japanese traditional male underwear) or 3 shaku obi sash (Japanese traditional female belt), and so on.

In case of the manufacturing textile such as towel, the density of the produced towel is defined by the number of the reeds per 1 sun of the kujira-jaku (about 3.787 centimeters).

The Gofuku-jaku (also known as Gofuku-zashi)

About 36.4 centimeters (1 shaku 2 sun in the kane-jaku)

It was mainly used for clothing related measurement. A variant unit of the kujira-jaku. A theory suggests that it was derived from the 5-bu shorter kujira-jaku.

The Kane-jaku (In the Meiji Measurement Regulation)

About 30.3 centimeters (defined as 10 over 33 meters)

Established in Meiji period in order to unify the matashiro-jaku, the kyoho-jaku, the setchu-jaku, and so on. In general, simply 'shaku' refers to the kane-jaku.

The Conversion with Other Traditional System of Weights and Measures

1 shaku is equivalent of the following lengths.

10 sun

1 over 10 Jo

1 over 6 Ken

The unit used for land area is tsubo (or bu) which is equivalent of the land area of 6 shaku square. Sho, the unit used for the volume of an object, is also based on the shaku unit.

[Original Japanese]