Japanese units of measurement

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is the traditional Japanese system of measurement. The name shakkanhō originates from the name of two of the units, the shaku, a length measurement, 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 stablized 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.

From 1924, the shakkanhō system was replaced by the metric system, and use of the old units for official purposes was forbidden after the 31^st of March 1966. However, in several instances the old system is still used. In carpentry and agriculture use of the old fashioned terms is common. Japanese chisels are manufactured in sizes of sun and bu. Modern Japanese bathrooms are built in sizes which are fractions of a tsubo, usually either 3/4, 1, or 1 1/4 of a tsubo and land is sold on the basis of price in tsubo. The 2005 Japanese census allowed 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.

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 inches), 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 different shaku developed for various purposes. The unit now most widely recognized as a shaku in Japan is the , shaku, the system shown in the table below. Kanejaku means "carpenter's square", and this shaku was the one used by Japanese carpenters. The carpenter's shaku, used for construction, preserved the original Chinese shaku measure, because it was never interfered with, whereas the other shaku systems, which were used for taxation or trade, were interfered with in order to increase taxation, and hence gradually varied from the original value.

The , literally "whale shaku", was a standard used in the clothing industry. The name "whale shaku" comes from the measuring rulers used, which were made from baleen. A kujirajaku is 1 1/4 the length of a kanejaku.

As well as the kanejaku and kujirajaku system, various other shaku systems also exist, for example the gofukujaku (呉服尺), where gofuku means traditional Japanese clothes, such as kimonos. In the gofukujaku system, one shaku is equal to 1.2 times the kanejaku's shaku.

In 1891, the lengths of the two most common shaku were defined in terms of the metric system:

1891 definitions	Kanji	Metric value	English equivalent
1 jō	丈	100/33 m	119.3 in
1 kanejaku	曲尺	10/33 m	11.93 in
1 kujirajaku	鯨尺	25/66 m	14.9 in

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 , 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 on in the name of the bamboo flute , literally "shaku eight", which is one shaku and eight sun in length, and the Japanese version of the Tom Thumb story, , literally "one sun boy", as well as in many Japanese proverbs.

The Shōsōin in Nara has an ivory one-shaku ruler, the .

Table of length units
Other units	Kanji	Relative value	Metric value	English value	Notes
mō	毛, 毫	1/1000 sun	0.03030 mm	0.001193 in
rin	厘	1/100 sun	0.3030 mm	0.01193 in
bu	分	1/10 sun	3.030 mm	0.1193 in
sun	寸	10 bu, 1/10 shaku	3.030 cm	1.193 in
shaku	尺	10 sun	30.30 cm	11.93 in
ken	間	6 shaku	1.818 m	71.57 in
hiro	尋	6 shaku	1.818 m	71.57 in	A unit of depth
jō	丈	10 shaku	3.030 m	119.3 in
chō	町	60 ken	109 m	358 ft
ri	里	36 chō	3.927 km	2.44 miles

The smallest units, mō, rin, and bu, are actually the names of fractions, 1/1,000, 1/100, and 1/10, respectively, which are also used as fractional units.

Area

The tsubo, which is essentially the area of two tatami mats, is still commonly used in discussing land pricing in Japan. The larger units are also commonly used by Japanese farmers for discussing the sizes of fields, perhaps because most farmers in Japan are members of the older generation.

Table of area units
Unit	Kanji	Equivalent value	Metric value	English units	Notes
1 shaku	勺	1/10 gō	330.58 cm²	51.24 in²
1 gō	合	1/10 tsubo	0.33058 m²	512.4 in²
1 tsubo	坪	1 square ken	3.3058 m²	35.584 ft²	Used in construction etc.
1 bu	歩	1 square ken	3.3058 m²	35.584 ft²	Used in agriculture.
1 se	畝	30 tsubo 3,000 go	99.1736 m²	1067.50 ft²
1 tan	段, 反	10 se	991.736 m²	0.2451 acres
1 chō or chōbu	町	10 tan	9,917.36 m²	2.4506 acres

Volume

1891 definition
shō = 2401/1331 litre (l) = 64.827 sun³

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

Table of volume units
Unit	Kanji	Equivalent value	Metric value	U.S. equivalents	Imperial equivalents	Notes
shaku	勺		18.039 ml	0.6100 fluid ounces	0.6349 fl oz.
gō	合	10 shaku	180.39 ml	6.100 fl oz	6.349 fl oz	A common size of serving of sake.
shō	升	10 gō	2401/1331 litres (exactly) 1.8039 l	61.00 fl oz	63.49 fl oz	A common size for sake bottles.
to	斗	10 shō	18.039 l	4.77 gal	3.968 gal
koku	石	10 to	180.39 l	40.95 (dry) gal or 5.12 bushels	39.68 gal or 4.96 bushels	Originally a volume of rice eaten in one year.

Mass

1891 definition
1 momme = 15/4 gram (g)

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

Table of units of mass
Unit	Kanji	Equivalent value	Metric value	Notes
1 fun	分		375 mg
1 momme	匁	10 fun	3.75 g
hyakume	百目	100 momme	375 g	Hyakume means "100 me"
1 kin	斤	160 momme	600 g
1 kan or kanme	貫, 貫目	1,000 momme	3.75 kg

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", in other words "Early to bed, early to rise makes a man healthy, wealthy, and wise."

Table of money units
Unit	Kanji	Equivalent to
1 mon	文
1 hiki		10 mon
1 kanmon	貫文	100 hiki

Other Japanese 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:

• Japanese bicycles are based on a British system, and the tyre sizes are measured in inches rather than centimetres.
• Inch sizes are commonly used in the computer industry for the sizes of parts, connectors, and semiconductor wafers.
• Inches and feet are used for the width and length of magnetic tape.
• Inches are used for the size of television screens. Because inches are not a legally recognized unit in Japan, instead of writing the word "inch", Japanese companies substitute "-gata" (型). Thus, a television with a 17 in diagonal measure is described as 17型.
• The sizes of photographic prints are based on the inch, though rounded to the nearest millimetre.

References

• The current Japanese law on measurement (in Japanese) [link]

External links

• [Japanese units] (in Japanese)
• [Japanese carpenter's square] at the [Takenaka carpentry tools museum].

See also

• History of measurement
• Units of measurement
• Chinese unit
• Metrication
• Japanese clock
• Japanese counter word
• Japanese numerals

 

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