The system is of chinese origins, similar to almost everything in japanese culture. The units of measurement originated in the Shang Dynasty during the 13th century BC and stabilized during the Zhou Dynasty in the 10th century BC spreading to Japan. The units of the Tang Dynasty eventually spread to Japan in 701 AD, and the current shaku measurement has hardly altered since.
1891 definitionsUnitDefinitionConversionsRomanizedKanjiLengthmetresmetresinchesfeetyards1 jō丈100⁄333.030 119.3 9.942 3.314 1 kanejaku曲尺10⁄330.303011.930.99420.3314VolumelitreslitresmillilitresUSfluid ouncesImperialfluid ouncesshō升2401⁄13311.804 1804 61.00 63.49 Massgramsgramsdramsouncespounds1 momme匁15⁄43.75 2.116 0.1323 8.267 × 10-3Note: Definitions are exact and conversions are rounded to four significant figures.
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 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 different shaku developed for various purposes. The unit of the base of all measurement, such as area is shaku. To distinguish from other variants of shaku, this unit is called the kanejaku (曲尺?). 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.