Japanese units of measurement

Shakkan-hō (尺貫法) is the traditional Japanese system of measurement. The name shakkanhō originates from the name of two of the units, the shaku, a unit of length, and the kan, a mass 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 from 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. Until the 2005 Japanese census, people were able to give the area of their houses in either square metres or tsubo. The tsubo was not used in the 2010 census.

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:

1891 definitions

Unit		Definition	Conversions
Romanized	Kanji
Length		metres	metres	inches	feet	yards
jō	丈	100⁄33	3.03	119.3	9.942	3.314
kanejaku	曲尺	10⁄33	0.303	11.93	0.9942	0.3314
Volume		litres	litres	millilitres	US fluid ounces	Imperial fluid ounces
shō	升	2401⁄1331	1.804	1804	61.00	63.49
Mass		grams	grams	drams	ounces	pounds
momme	匁	15⁄4	3.75	2.116	0.1323	0.008267
Note: Definitions are exact and conversions are rounded to four significant figures.

Length

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 7.1 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.

The Shōsōin in Nara has ivory one-shaku rulers, the kōgebachiru-no-shaku (紅牙撥鏤尺).

Table of Lengths

Unit		shaku	Metric		Imperial/US
Romanized	Kanji		millimetres	metres	inches	feet	yards
mō	毛, 毫	1⁄10000	0.03030	3.030×10−5	1.193×10−3	9.942×10−5	3.314×10−5
rin	厘	1⁄1000	0.3030	3.030×10−4	0.01193	9.942×10−4	3.314×10−4
bu	分	1⁄100	3.030	3.030×10−3	0.1193	9.942×10−3	3.314×10−3
sun	寸	1⁄10	30.30	0.03030	1.193	0.09942	0.03314
shaku	尺	1	303.0	0.3030	11.93	0.9942	0.3314
ken	間	6	1818	1.818	71.58	5.965	1.988
hiro	尋	6	1818	1.818	71.58	5.965	1.988
jō	丈	10	3030	3.030	119.3	9.942	3.314
chō	町	360	1.091×105	109.1	4295	357.9	119.3
ri	里	12,960	3.927×106	3927	1.546×105	1.288×104	4295
Notes: Conversions to metric, imperial and US customary units are rounded to four significant figures. The smallest units, mō, rin and bu, are actually the names of fractions, 1⁄10000, 1⁄1000 and 1⁄100, respectively, which are also used as fractional units. The shaku is, in some cases, the Japanese equivalent to the foot. The hiro is a unit of depth—the Japanese equivalent of the fathom. 1 chō = 60 ken ˜ 0.1091 kilometres ˜ 0.06779 miles 1 ri = 36 chō ˜ 3.927 kilometres ˜2.440 miles

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.

Area

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.

Table of area units

Unit		tsubo	Metric	Imperial/US
Romanized	Kanji		square metres	square inches	square feet	square yards
shaku	勺	1⁄100	0.03306	51.24	0.3558	0.03954
gō	合	1⁄10	0.3306	512.4	3.558	0.3954
jō	畳	1⁄2	1.653	2562	17.79	1.979
tsubo	坪	1	3.306	5124	35.58	3.954
bu	歩	1	3.306	5124	35.58	3.954
se	畝	30	99.17	1.537×105	1067	118.6
tan	段, 反	300	991.7	1.537×106	1.067×104	1186
chō	町, 町歩	3000	9917	1.537×107	1.067×105	1.186×104
Notes: Conversions to metric, imperial and US customary units are rounded to four significant figures. A jō is the size of one tatami mat-used in quoting room sizes. 1 tsubo = 1 square ken-used in construction. 1 bu = 1 square ken-used in agriculture. 1 tan ≈ 0.09917 hectares ≈ 0.2451 acres 1 chō ≈ 0.9917 hectares ≈ 2.451 acres

Volume

A sake cup (1 gō ) for celebrations

These units are still used, for example, in sake production.

Table of volume units

Unit		shō	Metric		US liquid measure			Imperial
Romanized	Kanji		millilitres	litres	fluid ounces	pints	gallons	fluid ounces	pint	gallons
sai	才	1⁄1000	1.804	1.804×10−3	0.06100	3.812×10−3	4.765×10−4	0.06349	3.174×10−3	3.968×10−4
shaku	勺	1⁄100	18.04	0.01804	0.6100	0.03812	4.765×10−3	0.6349	0.03174	3.968×10−3
gō	合	1⁄10	180.4	0.1804	6.100	0.3812	0.04765	6.349	0.3174	0.03968
shō	升	1	1804	1.804	61.00	3.812	0.4765	63.49	3.174	0.3968
to	斗	10	1.804×104	18.04	610.0	38.12	4.765	634.9	31.74	3.968
koku	石	100	1.804×105	180.4	6100	381.2	47.65	6349	317.4	39.68
Notes: Conversions to metric, imperial and US customary units are rounded to four significant figures. The gō is a common size for serving sake. The shō (about 64.827 cubic sun) is a former common sake-bottle size (it is presently legally filled and labelled as 1800 mL). The koku (about 40.95 US dry gal) originally was the volume of rice a person would eat in one year.

Mass

The Japanese unit of mass, momme, is a recognized unit in the international pearl industry.

Table of units of mass

Unit		momme	Metric			Avoirdupois
Romanized	Kanji		milligrams	grams	kilograms	drams	ounces	pounds
fun	分	1⁄10	375	0.375	3.75×10−4	0.2116	0.01323	8.267×10−4
momme	匁	1	3750	3.75	3.75×10−3	2.116	0.1323	8.267×10−3
hyakume	百目	100	3.75×105	375	0.375	211.6	13.23	0.8267
kin	斤	160	6×105	600	0.6	338.6	21.16	1.323
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.

Money

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."

Table of money units

Unit		Equivalent to
Romanized	Kanji
1 mon	文
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. For example, the inch is 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 and monitor/phone screens. However, the word 型 ("-gata") is substituted for インチ ("inch") on televisions. 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
• Metrication
• Japanese clock
• Japanese counter word
• Japanese numerals
• Related Units of measurement
  • Chinese units of measurement
  • Taiwanese units of measurement
  • Hong Kong units of measurement

External links

• Japanese Carpentry Museum
• Japanese units Template:Ja icon
• 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