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Japanese units of measurement

Traditional Japanese units of measurement or the shakkanhō (尺貫法, "shaku–kan system") 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 AD 701.[citation needed] Following the 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, owing to their occupations by the Japanese.

For a time in the early 20th century, the traditional, metric, and English 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 in carpentry and agriculture, with tools such as chisels, spatels, saws, hammers manufactured in sun and bu sizes. Floorspace is reckoned in terms of tatami mats and land is sold on the basis of price in tsubo. Many rice cookers are sold with measuring cups of 1 .



Customary Japanese units are a local adaption 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.[1] It received its prototype metre and kilogram from the International Bureau of Weights and Measures in 1890.[1] 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.[1] The law codified the values of the traditional and metric units in terms of one another,[1] but retained the traditional units as the formal standard and metric values as secondary.[2]

1891 definitions
Unit Definition Conversions
Romanised Kanji
Length metres metres feet
shaku 1033 0.3030 0.9942
Area square
tsubo 10030¼ 3.306 35.58
Volume litres litres US
shō 24011331 1.804 0.4765 0.3968
Mass kilograms kilograms pounds
kan 154 3.750 8.267
Note: Definitions are exact and conversions are rounded to four significant figures.

In 1909, English units were also made legal within the Empire of Japan.[1] 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.[1] Upon its advice, the Imperial Diet established the metric system as Japan's legal standard, effective 1 July 1924,[3] with use of the other systems permitted as a transitional measure.[1] The government and "leading industries" were to convert within the next decade, with others following in the decade after that.[4] Public education—at the time compulsory through primary school—began to teach the metric system.[4] 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.[4] 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.[4] 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.[4]

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.[5] 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.[5] 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.[5] 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.[6]

With the majority of the public now exposed to it since childhood,[4] the metric system became the sole legal measurement system in most fields of Japanese life on 1 January 1959.[1] Redrafting of laws to use metric equivalents had already been accomplished but conversion of the land registries required until 31 March 1966 to accomplish.[7][6] Industry transitioned gradually at its own expense, with compliance sometimes being nominal, as in the case of ¼-inch screws becoming "¼ screws".[8] 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 reckoned at only 85%.[9] 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.[8]

Some use of the traditional units continues. Some Japanese describe their weight in terms of kan.[8] 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.[citation needed] English units continue to be employed in aviation,[9] munitions,[9] and various sports, including golf and baseball.[8]


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 reckoned from the end of the thumb to the tip of an outstretched middle finger but gradually increased in length to about a third of metre, closer to the size of a foot.

As in China and Korea, Japan employed different shaku 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"[11] or "whale" shaku (鯨尺, kujirajaku), named for tailors' and fabric merchants' baleen rulers, was ¼ longer[11] and used in measuring cloth. (A longer unit of about 25 cloth shaku was the tan.)[11] Traditional Japanese clothing was reckoned using the "traditional clothing" shaku (呉服尺, gofukujaku), about ​15 longer than the carpentry shaku. The Shōsōin in Nara has ivory 1-shaku[which?] rulers, the kōgebachiru-no-shaku (紅牙撥鏤尺).

The Japanese ri is now much longer than the Chinese or Korean li, comprising 36 chō, 2160 ken,[12] or 12,960 shaku. A still longer unit was formerly standard in Ise on Honshu and throughout the 9 provinces of Kyushu, which comprised 50 chō, 3000 ken,[12] or 18,000 shaku. The imperial nautical mile of 6080 feet (1853.19 m) was also formerly used by the Japanese in maritime contexts as a "marine ri".[11] 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]

Table of Lengths
Unit Shaku[11] Metric US & Imperial
Romanised Kanji Exact Approx. Exact Approx.
or  ​110000  1/33,000 m 0.03030 mm 5/150,876 yd 0.001193 in
Rin 11000  1/3300 m 0.3030 mm 25/75,438 yd 0.01193 in
Bu 1100  1/330 m 3.030 mm 125/37,719 yd 0.1193 in
Sun 110  1/33 m 3.030 cm 1250/37,719 yd 1.193 in
Shaku 10/33 m 30.30 cm 12,500/37,719 yd 11.93 in
Ken[b] 60/33 m 1.818 m 25,000/12,573 yd 5 ft 11.6 in
10  100/33 m 3.030 m 125,000/37,719 yd 9 ft 11.3 in
Chō[c] 360  3600/33 m 109.1 m 500,000/4191 yd 357 ft 11 in
Ri[d] 12,960  129,600/33 m 3.927 km 6,000,000/1397 yd 2.440 mi
  • 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 names
    for 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 5 Shaku[11] (1.5152 meters).

The traditional 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.


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 , the area of the Nagoya tatami mat. Both units are used informally in discussing real estate floorspace. Due to historical connections, the tsubo is still used as the official base unit of area in Taiwan.

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
Unit Tsubo Metric US & Imperial
Romanized Kanji Exact Approx. Exact Approx.
Shaku 1100 4/121  330.6 cm² 6,250,000/158,080,329 yd² 51.24 in²
110 40/121  0.3306  62,500,000/158,080,329 yd² 3.558 ft²
12 200/121  1.653  312,500,000/158,080,329 yd² 17.79 ft²
Tsubo 1 400/121  3.306  625,000,000/158,080,329 yd² 35.58 ft²
Se 30 12,000/121  99.17  6,250,000,000/52,693,443 yd² 1067 ft²
Tan or 300 120,000/121  991.7  62,500,000,000/52,693,443 yd² 10,670 ft²
Chō(bu)[e] () 3000 1,200,000/121  0.9917 ha 625,000,000,000/52,693,443 yd² 2.449 acres
  • Approximations are rounded to four significant figures.


A sake cup (1 ) for celebrations

The base unit of Japanese volume is the shō, although the now sees more use since it is reckoned as the appropriate size of a serving of rice or sake. Sake bottles are now marketed as containing 1800 mL exactly.

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.[citation needed] The koku of rice was sometimes reckoned as 3000 "sacks".[12] By the 1940s the shipping koku was ​110 of the shipping ton[11] of 40 or 42 ft³ (i.e., 110–120 L); the koku of timber was about 10 ft³ (280 L);[11] and the koku of fish, like many modern bushels, was no longer reckoned by volume but computed by weight (40 kan).[11] The shakujime of timber was about 12 ft³ (340 L) and the taba about 108 ft³ (3,100 L or 3.1 m3).[11]

Table of volume units
Unit Shō Metric US Imperial
Romanized Kanji Exact Approx. Exact Approx. Exact Approx.
Sai 11000 2401/1,331,000 L 1.804 mL 37,515,625/15,900,351,812,136 yd³ 29.28 min 240,100/605,084,579 gal 30.47 min
0.1101 in³
Shaku 1100 2401/133,100 L 18.04 mL 187,578,125/7,950,175,906,068 yd³ 0.6100 fl oz 2,401,000/605,084,579 gal 0.6349 fl oz
1.101 in³
110 2401/13,310 L 180.4 mL 937,890,625/3,975,087,953,034 yd³ 0.3812 pt 24,010,000/605,084,579 gal 0.3174 pt
0.3276 dry pt
Shō 1 2401/1331 L 1.804 L 4,689,453,125/1,987,543,976,517 yd³ 1.906 qt 240,100,000/605,084,579 gal 1.587 qt
1.638 dry qt
To 10 24,010/1331 L 18.04 L 46,894,531,250/1,987,543,976,517 yd³ 4.765 gal 2,401,000,000/605,084,579 gal 3.968 gal
2.048 pk
Koku[f] 100 240,100/1331 L 180.4 L 468,945,312,500/1,987,543,976,517 yd³ 47.65 gal 24,010,000,000/605,084,579 gal 39.680 gal
5.119 bu
  • Approximations are rounded to four significant figures.


The base unit of Japanese weight or mass is the kan, although the momme is in more common use. It is a recognized unit in the international pearl industry.

The Japanese form of the Chinese tael was the ryō ().[g] It was customarily reckoned as around 4 or 10 momme[12] but, because of its importance as a fundamental unit of the silver and gold bullion used as currency in medieval Japan, it varied over time and location from those notional values.

Table of units of mass
Unit Kan[17] Metric US & Imperial
Romanized Kanji Legal Decimal Exact Approx.
or 11,000,000 3/800,000 kg 3.75 mg 375/45,359,237 lb 8.267 μlb
Rin 1100,000 3/80,000 kg 37.5 mg 3750/45,359,237 lb 0.5787 gr
Fun[h] 110,000 3/8000 kg 375 mg 37,500/45,359,237 lb 5.787 gr
11000 3/800 kg 3.75 g 375,000/45,359,237 lb 2.116 dr
Hyakume 百目 110 3/8 kg 375 g 37,500,000/45,359,237 lb 13.23 oz
Kin[j] 425 3/5 kg 600 g 60,000,000/45,359,237 lb 1.323 lb
Kan(me)[k] () 1 15/4 kg 3.75 kg 375,000,000/45,359,237 lb 8.267 lb
Maru 8 30 kg 3,000,000,000/45,359,237 lb 66.14 lb
Tan[l] or 16 60 kg 6,000,000,000/45,359,237 lb 132.3 lb
  • Exact figures follow the 1891 Law of Weights & Measures and 1959 International Yard and Pound Agreement.
  • Metric values are exact. US & imperial approximations are rounded to four significant figures.

English unitsEdit

English units—both US and imperial—see use in some Japanese contexts. Feet and inches are used for most non-sport bicycles, whose tire sizes follow a British system; for sizes of magnetic tape and many pieces of computer hardware; for photograph sizes; and for the sizes of display screens for electronic devices. Photographic prints, however, are usually rounded to the nearest millimetre and screens are not described in terms of inches but "type" (, gata). For instance, a television whose screen has a 17-inch diagonal is described as a "17-type" (17) and one with a 32-inch widescreen screen is called a "32-vista-type" (32V).

See alsoEdit


  1. ^ In the 10th lunar month of the 3rd year of Meiji (around November 1871), the Railways Ministry defined the "English foot" as 1 shaku 4 rin, making the shaku equivalent to about 0.996 ft.[10]
  2. ^ The ken[13] is also found in English sources as the kin or glossed as the Japanese fathom.[12]
  3. ^ The chō is also found in English sources as the cho or tsyo.[12]
  4. ^ The Japanese ri is also frequently known by its Chinese name li[12] or glossed as the Japanese mile.[14]
  5. ^ Chōbu is used rather than chō when no fraction follows.[citation needed]
  6. ^ The koku has also appeared in English as the kokf and its multiples as the ikwankokf or ickmagog (1000 koku) and man-kokf or managoga (10,000 koku).[12]
  7. ^ The ryō is sometimes written in English as ryo, without its macron.[15] It also appears in English sources as the tael,[16] the táīl, the táhil, and the táïl.[12]
  8. ^ The fun is more often known in English as the candareen.[18] It also sometimes appears as the kondúrí or konderi.[12]
  9. ^ Although monme is the Revised Hepburn romanization of the unit, momme is more common in English.[19] It also sometimes appears as the mommé, me,[citation needed] or mas.[12]
  10. ^ Particularly in historical sources, the kin is more commonly known in English as the catty[20] or katí.[12]
  11. ^ The kan is also sometimes known in English as the kwan.[11]
  12. ^ Particularly in historical sources, the tan is more commonly known in English as the picul,[21] pikul, or pikel.[12]



  1. ^ a b c d e f g h Tamano (1971), p. 97.
  2. ^ Lyon (1901), p. 933.
  3. ^ "改正度量衡法規", Digital Collections, Tokyo: National Diet Library . (in Japanese)
  4. ^ a b c d e f Tamano (1971), p. 98.
  5. ^ a b c Tamano (1971), p. 99.
  6. ^ a b Tamano (1971), p. 100.
  7. ^ "メートル条約", Official site, Ibaraki: International Metrology Cooperation Office, Archived from the original on 9 March 2012  . (in Japanese)
  8. ^ a b c d Tamano (1971), p. 101.
  9. ^ a b c Tamano (1971), p. 102.
  10. ^ 日本鉄道史 [Nippon Tetsudō-shi, Japanese Railway History], Vol. I, Tokyo: Ministry of Railways, 1921, p. 49 . (in Japanese)
  11. ^ a b c d e f g h i j k USWD (1944), p. 400.
  12. ^ a b c d e f g h i j k l m Renouard (1845), p. 486.
  13. ^ OED, "ken, n.³".
  14. ^ Renouard (1845), p. 490.
  15. ^ OED, "ryo, n.".
  16. ^ OED, "tael, n.".
  17. ^ Nagase-Reimer (2016), p. xiii.
  18. ^ OED, "candareen, n.".
  19. ^ OED, "momme, n.".
  20. ^ OED, "catty, n.¹".
  21. ^ OED, "picul, n.".


External linksEdit