Traditional Japanese units of measurement or the shakkanhō () is the traditional system of measurement used by the people of the Japanese archipelago. It is largely based on the Chinese system, which spread to Japan and the rest of the Sinosphere in antiquity. It has remained mostly unaltered since the adoption of the measures of the Tang dynasty in 701. Following the 1868 Meiji Restoration, Imperial Japan adopted the metric system and defined the traditional units in metric terms on the basis of a prototype metre and kilogram. The present values of most Korean and Taiwanese units of measurement derive from these values as well.

In the early 20th century, the traditional system, the metric system, and the Imperial system 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 in carpentry and agriculture, with tools such as chisels, spatels, saws, and hammers manufactured in sun and bu sizes. Floorspace is expressed in terms of tatami mats, and land is sold on the basis of price in tsubo. Sake is sold in multiples of 1gō, with the most common bottle sizes being 4 (720 mL) or 10 (1.8 L, isshōbin).

History Customary Japanese units are a local adaptation of the traditional 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.

Japan signed the Treaty of the Metre in 1885, with its terms taking effect in 1886. It received its prototype metre and kilogram from the International Bureau of Weights and Measures in 1890. The next year, a weights and measurements law codified the Japanese system, taking its fundamental units to be the shaku and kan and deriving the others from them. The law codified the values of the traditional and metric units in terms of one another, but retained the traditional units as the formal standard and metric values as secondary.

+ 1891 definitionsUnitDefinitionConversionsRomanisedKanjiLengthmetresmetres feet shaku 0.303 0.9942Areasquaremetres squaremetres squarefeet tsubo 3.306 35.58VolumelitreslitresUSgallonsImperialgallons shō 1.804 0.4765 0.3968Masskilogramskilograms pounds kan 3.750 8.267Note: Definitions are exact and conversions are rounded to four significant figures.

In 1909, English units were also made legal within the Empire of Japan. Following World War I, the Ministry 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. Upon its advice, the Imperial Diet established the metric system as Japan's legal standard, effective 1 July 1924,. with use of the other systems permitted as a transitional measure. The government and "leading industries" were to convert within the next decade, with others following in the decade after that.. Public education—at the time compulsory through primary school—began to teach the metric system. 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. 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. 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.

Following its defeat in World War II, Japan was occupied by America and saw an expanded use of US customary units. Gasoline was sold by the gallon and cloth by the yard.. 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. An unofficial and ad 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. Its first success was the conversion of candy sales in Tokyo department stores from the momme to the gram in September 1956; others followed, with NHK taking the lead in media use..

With the majority of the public now exposed to it since childhood, the metric system became the sole legal measurement system in most fields of Japanese life on 1 January 1959.. Redrafting of laws to use metric equivalents had already been accomplished, but conversion of the land registries required until 31 March 1966 to complete.. Industry transitioned gradually at its own expense, with compliance sometimes being nominal, as in the case of screws becoming " screws".. 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%.. 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 noting shaku and sun) were criminalised after 1961.

Some use of the traditional units continues. Homes continue to be reckoned in terms of tsubo, even on the national census as late as 2005, although the practice was discontinued in 2010. English units continue to be employed in aviation, munitions, and various sports, including golf and baseball.

Length

The base unit of Japanese length is the shaku based upon the Chinese chi, with other units derived from it and changing over time based on its dimensions. The chi was originally a span taken from the end of the thumb to the tip of an outstretched middle finger, but which gradually increased in length to about , just a few centimetres longer than the size of a foot.

As in China and Korea, Japan employed different shaku for different purposes. The "carpentry" shaku (, kanejaku) was used for construction. It was a little longer in the 19th century prior to its metric redefinition. The "cloth" or "whale" shaku (, kujirajaku), named for tailors' and fabric merchants' baleen rulers, was longer and used in measuring cloth. (A longer unit of about 25cloth shaku was the tan.) Traditional Japanese clothing was reckoned using the "traditional clothing" shaku (, gofukujaku), about longer than the carpentry shaku. The Shōsōin in Nara has ivory 1-shaku rulers, the .

The Japanese ri is now much longer than the Chinese or Korean li, comprising 36 chō, 2160 ken,. or 12,960shaku. A still longer unit was formerly standard in Ise on Honshu and throughout the 9 provinces of Kyushu, which comprised 50 chō, 3000 ken, or 18,000shaku. The imperial nautical mile of 6080feet (1853.19m) was also formerly used by the Japanese in maritime contexts as a "marine ri".. A fourth and shorter ri of about 600m 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.

+ Table of LengthsIwata, Shigeo. "Weights and Measures in Japan"UnitShaku Metric US & ImperialRomanisedKanjiExactApprox.ExactApprox. Mō or    m 0.03030mm yd 0.001193in Rin or   m 0.3030mm yd 0.01193in Bu   m 3.030mm yd 0.1193in Sun   m 3.030cm yd 1.193in Shaku 1   m 30.30cm yd 11.93in Ken 6   m 1.818m yd 5ft11.6in Hiro Jō 10   m 3.030m yd 9ft11.3in Chō 360   m 109.1m yd 357ft11in Ri 12,960  m 3.927km yd 2.440miNotes: Exact figures follow the 1891 Law of Weights & Measures and 1959 International Yard and Pound Agreement. Approximations are rounded to four significant figures. The names of the smallest units, borrowed from Chinese, also function as the Japanese namesfor the fractions "hundredth", "thousandth", and "ten-thousandth". The ken is the normal unit of distance and length; the hiro used as the equivalent unit of depth. Sometimes hiro is used equal to 5shaku (m, ~1.5152 metres).

The traditional units are still used for construction materials in Japan. For example, plywood is usually manufactured in (about ) sheets known in the trade as , 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 , literally "shaku eight", which measures one shaku and eight sun, and the Japanese version of the Tom Thumb story, , literally "one sun boy", as well as in many Japanese proverbs.

Area

The base unit of Japanese area is the tsubo, equivalent to a square ken or 36 square shaku. It is twice the size of the jō, the area of the Nagoya tatami mat. Both units are used informally in discussing real estate floorspace. Tsubo is a square ken. Gyllenbok says that the size of tatami or jo became “standardized in the Muromachi Period (1338–1573) at one ken long and half a ken wide. The ken, however, has varied over the centuries. It is now generally about 1.82m, but reaches 1.97m in the Kansai area, including the cities of Kyoto, Osaka, and Kobe. Thus, one tatami is about 1.62 to 1.95m.” Due to historical connections, the tsubo is still used as a unit of area in real estate in Taiwan, where it is called the píng.

In agricultural contexts, the tsubo is known as the bu. The larger units remain in common use by Japanese farmers when discussing the sizes of fields.

+ Table of area units UnitTsuboMetricUS & ImperialRomanizedKanjiExactApprox.ExactApprox. Shaku m2 330.6cm2 sqyd 51.24sqin Gō m2 0.3306m2 sqyd 3.558sqft Jō or m2 1.653m2 sqyd 17.79sqft Tsubo 1 m2 3.306m2 sqyd 35.58sqft Bu Se 30 m2 99.17m2 sqyd 1,067sqft Tan or 300 m2 991.7m2 sqyd 10,674.6sqft Chō(bu) () 3000 m2 0.9917ha sqyd 2.4505acresNotes: Approximations are rounded to four significant figures.

Volume

The base unit of Japanese volume is the shō, although the gō now sees more use since it is reckoned as the appropriate size of a serving of rice or sake. Sake and shochu are both commonly sold in large 1800mL bottles known as , literally "one shō bottle".

The koku 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. The koku of rice was sometimes reckoned as 3000"sacks". By the 1940s the shipping koku was of the shipping ton of 40 or 42cuft (i.e., ); the koku of timber was about 10cuft (); and the koku of fish, like many modern bushels, was no longer reckoned by volume but computed by weight (40kan). The shakujime of timber was about 12cuft () and the taba about 108ft³ ( or ).

+ Table of volume units UnitShōMetricUSImperialRomanizedKanjiExactApprox.ExactApprox.ExactApprox. Sai L 1.804mL cuyd 29.28min gal 30.47min 0.1101cuin Shaku L 18.04mL cuyd 0.6100floz gal 0.6349floz 1.101cuin Gō L 180.4mL cuyd 0.3812pt gal 0.3174pt 0.3276drypt Shō 1 L 1.804L cuyd 1.906qt gal 1.587qt 1.638dryqt To 10 L 18.04L cuyd 4.765gal gal 3.968gal 2.048pk Koku 100 L 180.4L cuyd 47.65gal gal 39.680gal 5.119buNotes: Approximations are rounded to four significant figures.

Mass