Shaku (unit)

The shaku (Japanese: 尺) or Japanese foot is a Japanese unit of length derived (but varying) from the Chinese chi, originally based upon the length of the forearm (compare cubits). Traditionally, the length varied by location or use, but it is now standardized as ¹⁰/₃₃ meters (30.3 centimeters or 11.9 inches). The measurement also forms the basis of the modern Taiwanese chi.

Etymology

Shaku entered English in the early 18th century, deriving from the Japanese pronunciation of the kanji 尺, the same character as the Chinese chi. (The modern Taiwanese chi actually uses this length as well, while the mainland and Hong Kong chis vary slightly.)

Japan

1 shaku (Japan) =

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

The shaku has been standardized as ¹⁰/₃₃ meter (30.3 centimeters or 11.9 inches) since 1891. This means that there are 3.3 shaku to one meter. The use of the unit for official purposes was banned on March 31, 1966, although it is still used in traditional Japanese carpentry and some other fields. The traditional Japanese bamboo flute known as the shakuhachi ("shaku and eight") derives its name from its length of one shaku and eight sun. Similarly, the koku remains in use in the Japanese lumber trade.

Traditionally, the measurement varied over time, location, and use. By the early 19th century they were largely within the range of 0.30175 to 0.303 meters (11.880 in to 11.929 in), but a longer value of the shaku (also known as the kōrai-shaku) was 1.17 times longer than the present value (35.5 centimeters or 14.0 inches).

Kujirajaku

Another shaku variant used for measuring cloth, which was ¹²⁵/₃₃₀ meters (37.9 centimeters or 14.9 inches). It was called the "whale shaku" (鯨尺, kujirajaku), because baleen (whale whiskers) were used as cloth rulers.

To distinguish the two variants of shaku, the general unit was known as the "metal shaku" (金尺/曲尺, kanejaku). The Shōsōin in Nara preserves some antique ivory one-shaku rulers, known as the kōgebachiru-no-shaku (紅牙撥鏤尺).

Korea

1 ja (Korean: 자) =

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

In 1902, the Korean Empire adopted the Japanese definition of the shaku as that of the ja (자).

Derived units

Main: cun, zhang, ken, and koku.

Length

Just as with the Chinese unit, the shaku is divided into ten smaller units, known as sun (寸) in Japanese, and ten shaku together form a larger unit known in Japanese as a jō (丈). The Japanese also had a third derived unit, the ken, equal to 6 shaku; this was used extensively in traditional Japanese architecture as the distance between supporting pillars in Buddhist temples and Shinto shrines.

Volume

Ten cubic shaku comprised a koku, reckoned as the amount of rice necessary to sustain a peasant for a year.

See also

• Japanese units of measurement