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TraditionalJapanese units of measurement or theshakkanhō (尺貫法) is thetraditionalsystem of measurement used by the people of theJapanese archipelago. It is largely based on theChinese system, which spread to Japan and the rest of theSinosphere in antiquity. It has remained mostly unaltered since the adoption of the measures of theTang dynasty in 701.^[1] Following the 1868Meiji Restoration,Imperial Japanadopted themetric system and defined the traditional units in metric terms on the basis of aprototype metre andkilogram. The present values of mostKorean andTaiwanese units of measurement derive from these values as well.

For a time in the early 20th century, the traditional, metric, andEnglish systems were all legal in Japan. Although commerce has since been legally restricted to using the metric system, the old system is still used in some instances. The old measures are common incarpentry andagriculture, with tools such aschisels, spatels, saws, and hammers manufactured insun andbu sizes.Floorspace is expressed in terms oftatami mats, and land is sold on the basis of price intsubo.Sake is sold in multiples of 1 gō, with the most common bottle sizes being 4 (720 mL) or 10 (1.8 L,isshōbin).^[2]

Customary Japanese units are a local adaption of thetraditional Chinese system, which was adopted at a very early date. They were imposed and adjusted at various times by local and imperial statutes. The details of the system have varied over time and location in Japan's history.^[3]

Japan signed theTreaty of the Metre in 1885, with its terms taking effect in 1886.^[4] It received itsprototype metre andkilogram from theInternational Bureau of Weights and Measures in 1890.^[4] The next year, a weights and measurements law codified the Japanese system, taking its fundamental units to be theshaku andkan and deriving the others from them.^[4] The law codified the values of the traditional and metric units in terms of one another,^[4] but retained the traditional units as the formal standard and metric values as secondary.^[5]

In 1909,English units were also made legal within theEmpire of Japan.^[4] FollowingWorld War I, theMinistry of Agriculture and Commerce established a Committee for Weights and Measures and Industrial Standards, part of whose remit was to investigate which of Japan's three legal systems should be adopted.^[4] Upon its advice, the Imperial Diet established the metric system as Japan's legal standard, effective 1 July 1924,^[6] with use of the other systems permitted as a transitional measure.^[4] The government and "leading industries" were to convert within the next decade, with others following in the decade after that.^[7]Public education—at the time compulsory through primary school—began to teach the metric system.^[7] Governmental agencies and the Japanese Weights and Measures Association undertook a gradual course of education and conversion but opposition became vehemently outspoken in the early 1930s.Nationalists decried the "foreign" system as harmful to Japanese pride, language, and culture, as well as restrictive to international trade. In 1933, the government pushed the deadline for the conversion of the first group of industries to 1939; the rest of the country was given until 1954.^[7] Emboldened, the nationalists succeeded in having an Investigating Committee for Weights and Measures Systems established. In 1938, it advised that the government should continue to employ the "Shaku–Kan" system alongside the metric one.^[7] The next year, the imperial ordinance concerning the transition to the metric system was formally revised, indefinitely exempting real estate and historical objects and treasures from any need for metric conversion. The deadline for compulsory conversion in all other fields was moved back to 31 December 1958.^[7]

Followingits defeat inWorld War II, Japan wasoccupied by America and saw an expanded use ofUS customary units. Gasoline was sold by thegallon and cloth by the yard.^[8] The Diet revisited the nation's measurements and, with the occupation's approval, promulgated a Measurements Law in June 1951 that reaffirmed its intention to continue Japan's metrication, effective on the first day of 1959.^[8] An unofficial andad hoc Metric System Promotion Committee was established by interested scholars, public servants, and businessmen in August 1955, undertaking a public awareness campaign and seeking to accomplish as much of the conversion ahead of schedule as possible.^[8] Its first success was the conversion of candy sales in Tokyo department stores from themomme to the gram in September 1956; others followed, withNHK taking the lead in media use.^[9]

With the majority of the public now exposed to it since childhood,^[7] the metric system became the sole legal measurement system in most fields of Japanese life on 1 January 1959.^[4] Redrafting of laws to use metric equivalents had already been accomplished, but conversion of theland registries required until 31 March 1966 to complete.^[10][9] Industry transitioned gradually at its own expense, with compliance sometimes being nominal, as in the case of1⁄4-inch (6.35 mm) screws becoming "1⁄4 screws".^[11] Since the original fines for noncompliance were around$140 and governmental agencies mostly preferred to wait for voluntary conversion, metric use by December 1959 was estimated at only 85%.^[12] Since research showed that individual Japanese did not intend to actually use the metric units when given other options, however, sale and verification of devices marked with non-metric units (such as rulers and tape measures notingshaku andsun) were criminalised after 1961.^[11]

Some use of the traditional units continues. Some Japanese describe their weight in terms ofkan.^[11] Homes continue to be reckoned in terms oftsubo, even on thenational census as late as 2005, although the practice was discontinued in 2010.^{[citation needed]}English units continue to be employed in aviation,^[12]munitions,^[12] and various sports, includinggolf andbaseball.^[11]

The base unit of Japanese length is theshaku based upon the Chinesechi, with other units derived from it and changing over time based on its dimensions. Thechi was originally aspan taken from the end of the thumb to the tip of an outstretched middle finger, but which gradually increased in length to about1⁄3metre (33 cm), just a few centimetres longer than the size of afoot.^{[citation needed]}

As in China and Korea, Japan employed differentshaku for different purposes. The "carpentry"shaku (曲尺,kanejaku) was used for construction. It was a little longer in the 19th century prior to its metric redefinition.^[a] The "cloth"^[14] or "whale"shaku (鯨尺,kujirajaku), named for tailors' and fabric merchants'baleen rulers, was1⁄4 longer^[14] and used in measuring cloth. (A longer unit of about 25 clothshaku was thetan.)^[14]Traditional Japanese clothing was reckoned using the "traditional clothing"shaku (呉服尺,gofukujaku), about1⁄5 longer than the carpentryshaku. TheShōsōin inNara has ivory 1-shaku rulers, thekōgebachiru-no-shaku (紅牙撥鏤尺).^{[citation needed]}

The Japanese ri is now much longer than theChinese orKorean li, comprising 36chō, 2160ken,^[15] or 12,960 shaku. A still longer unit was formerly standard inIse onHonshu and throughout the9 provinces ofKyushu, which comprised 50chō, 3000ken,^[15] or 18,000 shaku. Theimperial nautical mile of 6080 feet (1853.19 m) was also formerly used by the Japanese in maritime contexts as a "marine ri".^[14] A fourth and shorter ri of about 600 m is still evident in some beach names. The "99-Ri" beach at Kujukuri is about 60 km. The "7-Ri" beach at Shichiri is 4.2 km long.^{[citation needed]}

The traditional units are still used for construction materials in Japan. For example, plywood is usually manufactured in182 cm × 91 cm (about72 in × 36 in) sheets known in the trade assaburokuhan (3 × 6版), or 3 × 6shaku. Each sheet is about the size of onetatami 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 fluteshakuhachi (尺八), literally "shaku eight", which measures oneshaku and eightsun, and the Japanese version of the Tom Thumb story,Issun Bōshi (一寸法師), literally "onesun boy", as well as in manyJapanese proverbs.^{[citation needed]}

The base unit of Japanese area is thetsubo, equivalent to a squareken or 36 squareshaku. It is twice the size of thejō, the area of the Nagoyatatami mat. Both units are used informally in discussing real estatefloorspace.^[20] Due tohistorical connections, the tsubo is still used as a unit ofarea in real estate in Taiwan, where it is called thepíng.^{[citation needed]}

In agricultural contexts, thetsubo is known as thebu. The larger units remain in common use by Japanese farmers when discussing the sizes of fields.^{[citation needed]}

The base unit of Japanese volume is theshō, although thegō now sees more use since it is reckoned as the appropriate size of aserving of rice orsake. Sake andshochu are both commonly sold in large 1800 mL bottles known asisshōbin (一升瓶), literally "oneshō bottle".^[21]

Thekoku is historically important: since it was reckoned as the amount of rice necessary to feed a person for a single year, it was used to compute agricultural output and official salaries.^{[citation needed]} Thekoku of rice was sometimes reckoned as 3000 "sacks".^[15] By the 1940s the shippingkoku was1⁄10 of theshipping ton^[14] of 40 or 42 cu ft (i.e., 110–120 L); thekoku of timber was about 10 cu ft (280 L);^[14] and thekoku of fish, like many modernbushels, was no longer reckoned by volume but computed by weight (40 kan).^[14] Theshakujime of timber was about 12 cu ft (340 L) and thetaba about 108 ft³ (3,100 L or 3.1 m³).^[14]

The base unit of Japanese mass is thekan, although themomme is more common. It is a recognised unit in the international pearl industry.^[22] In English-speaking countries, momme is typically abbreviated asmo.

The Japanese form of theChinesetael was theryō (両).^[f] It was customarily reckoned as around 4 or 10 momme^[15] but, because of its importance as a fundamental unit of the silver and goldbullion used ascurrency in medieval Japan, it varied over time and location from those notional values.^{[citation needed]}

Imperial units are sometimes used in Japan. Feet and inches are used for most non-sport bicycles, whose tyre sizes follow a British system; for sizes ofmagnetic tape and many pieces of computer hardware; for photograph sizes; and for the sizes of electronic displays for electronic devices.Photographic prints, however, are usually rounded to the nearest millimetre and screens are notdescribed in terms of inches but "type" (型,gata). For instance, a television whose screen has a 17-inch diagonal is described as a "17-type" (17型) and one with a 32-inchwidescreen screen is called a "32-vista-type" (32V型).^{[citation needed]}

• Japanese numerals,counter words,currency, &clocks
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• Oxford English Dictionary, Oxford: Oxford University Press.
• Iwata, Shigeo. "Weights and Measures in Japan" article in "Encyclopaedia of the History of Science, Technology, and Medicine in Non-Western Cultures".Encyclopaedia of the History of Science, Technology, and Medicine in Non-Western Cultures See Iwata's full table here:Encyclopaedia of the History of Science, Technology, and Medicine in Non-Western Cultures
• Gyllenbok, Jan. "Encyclopaedia of Historical Metrology, Weights and Measures", Vol 1.Encyclopaedia of Historical Metrology, Weights, and Measures
• "Japanese Weights, Measures, and Moneys",Handbook on Japanese Military Forces, Technical Manual E 30–480,Washington: US War Department, 1944, p. 400–1,ISBN 9780807164464{{citation}}:ISBN / Date incompatibility (help), reprinted by the Louisiana State University Press at Baton Rouge in 1991.
• Lyon, Samuel V. (1902),"Trade in 1901",Commercial Relations of the United States with Foreign Countries during the Year 1901,Vol. I,Washington: Bureau of Foreign Commerce, pp. 915–934.
• Tamano, Mitsuo (July 1971),"Japan's Transition to the Metric System",US Metric Study Interim Report,No. 3: Commercial Weights and Measures, National Bureau of Standards Special Publication 345-3,Washington: US Department of Commerce, pp. 97–102.
• Nagase-Reimer, Keiko (2016),Copper in the Early Modern Sino-Japanese Trade,Monies, Markets, and Finance in East Asia, 1600–1900, Vol. VII, Leiden: Brill,ISBN 9789004304512.
• Renouard, George Cecil (1845),"Japan",Encyclopaedia Metropolitana, or, Universal Dictionary of Knowledge,Vol. XX: Miscellaneous and Lexicographical,Vol. 7, London: B. Fellowes & al., pp. 470 ff.

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