Japanese units of measurement
The system is Chinese in origin. The units originated in the Shang Dynasty in the 13th century BC, and eventually stabilized in the Zhou Dynasty in the 10th century BC and spread from there to Japan, South East Asia, and Korea. The units of the Tang Dynasty were officially adopted in Japan in 701, and the current shaku measurement has hardly altered since then. Many Taiwanese units of measurement are derived form the shakkanhō system.
From 1924, the shakkanhō system was replaced by the metric system, and use of the old units for official purposes was forbidden after 31 March 1966. However, in several instances the old system is still used. In carpentry and agriculture use of the old-fashioned terms is common. Tools such as Japanese chisels, spatels, saws, hammers are manufactured in sizes of sun and bu. Land is sold on the basis of price in tsubo. The 2005 Japanese census freed people to give the area of their houses in either square metres or tsubo.
There are several different versions of the shakkanhō. The tables below show the one in common use in the Edo period. In 1891 the most common units were given definitions in terms of the metric system:
|Note: Definitions are exact and conversions are rounded to four significant figures.|
The basis of the shakkanhō length measurements is the shaku, which originated in ancient China. The other units are all fixed fractions or multiples of this basic unit. The shaku was originally the length from the thumb to the middle finger (about 18 cm or 7 in), but its length, and hence the length of the other units, gradually increased, since the length of the unit was related to the level of taxation.
Various shaku developed for various purposes. The unit of all measurement, such as area, is shaku. To distinguish from other shaku, this unit is called the kanejaku (曲尺). Kanejaku means "carpenter's square", and this shaku was used by Japanese carpenters. The carpenter's shaku, used for construction, preserved the original Chinese shaku measurement, because it was never altered, whereas the other shaku systems, which were used for taxation or trade, were altered to increase taxation, and, hence, gradually deviated from the original value.
The kujirajaku (鯨尺), literally "whale shaku", was a standard used in the clothing industry. The name, "whale shaku", comes from the rulers, which were made from baleen. A kujirajaku is 25% longer than kanejaku.
As well as the kanejaku and kujirajaku systems, other shaku systems also existed. One example is the gofukujaku (呉服尺), which refers to traditional Japanese clothing, such as kimonos. In the gofukujaku system, one shaku equals 1.2 times the kanejaku.
Shaku units are still used for construction materials in Japan. For example, plywood is usually manufactured in 182 cm × 91 cm (about 72 in × 36 in) sheets known in the trade as saburokuhan (3 × 6版), or 3 × 6 shaku. Each sheet is about the size of one tatami mat. The thicknesses of the sheets, however, are usually measured in millimetres.
The names of these units also live in the name of the bamboo flute shakuhachi (尺八), literally "shaku eight", which measures one shaku and eight sun, and the Japanese version of the Tom Thumb story, Issun Bōshi (一寸法師), literally "one sun boy", as well as in many Japanese proverbs.
Note: There is an older type of 'ri', about 600 m. This can be seen in use, for example, in beach names. Kujukuri Beach is 99 ri (kyu ju ku), about 60 km. Shichiri Beach is 7 ri (shichi) 4.2 km. While this use is evidence of the existence of the 'old' ri, information about it in English is hard to come by.
The tsubo, which is essentially the area of two standard sized tatami mats (tatami have an aspect ratio of 2:1, so two side by side form a square), is still commonly used in discussing land pricing in Japan. Note that actual tatami vary in size regionally, though legally the area of a tsubo is standardized. The larger units are also commonly used by Japanese farmers for discussing the sizes of fields. These units are practically equivalent to metric units of area which are for registrations of land, and no conversions are needed or colloquially used.
These units are still used, for example, in sake production.
|Unit||shō||Metric||US liquid measure||Imperial|
|Romanized||Kanji||millilitres||litres||fluid ounces||pints||gallons||fluid ounces||pint||gallons|
The Japanese unit of mass, momme, is a recognized unit in the international pearl industry.
|kan or kanme||貫, 貫目||1000||3.75×106||3750||3.75||2116||132.3||8.267|
|Note: Metric values are exact and conversions to avoirdupois units are rounded to four significant figures.|
The names of old money live on in Japanese proverbs such as haya oki wa san mon no toku, literally "Waking early gets you three mon", comparable to the English language proverb, "Early to bed, early to rise makes a man healthy, wealthy, and wise."
|1 hiki||疋||10 mon|
|1 kanmon||貫文||100 hiki|
Other units 
Apart from shakkanhō and the metric system, other units are also commonly used in Japan. The most common unit found is the inch. Inches are used in the following:
- The tyre sizes of bicycles, which are based on a British system
- In the computer industry, for the sizes of parts, connectors, and semiconductor wafers.
- Together with feet, for the width and length of magnetic tape.
- The sizes of television screens. However, the word 型 ("-gata") is substituted for インチ ("inch"). Thus, a television with a 17 inch diagonal measure is described as 17型.
- The sizes of photographic prints, though rounded to the nearest millimetre.
See also 
- History of measurement
- Japanese clock
- Japanese counter word
- Japanese numerals
- Related Units of measurement
- "改正度量衡法規". National Diet Library. Retrieved 7 July 2010.
- "メートル条約". International Metrology Cooperation Office. Retrieved 7 July 2010.
- Ministry of Railway (鉄道省 Tetsudō-shō ) ([大正10]). Japan Railway History (日本鉄道史 Nippon (or Nihon) Tetsudō-shi ) (in Japanese). 1 of 3 (上巻 Jōkan ). [Tokyo] : [Ministry of Railway]. p. 49. "In the 10th month of Meiji 3, probably November 1871, we defined 1 English foot of railway as 1 shaku 4 rin (1.004 shaku) of ours."
- "Chōbu" is used when no fraction follows
- Japanese Carpentry Museum
- Japanese units (Japanese)
- Convert traditional Japanese units to metric and imperial units (lengths, areas, volumes, weights) (sci.lang.Japan FAQ pages)
- Simple Japanese Traditional Area Units Converter
- Simple Japanese Distance and Length Units Converter