The shaku, unit of length
The shaku measures exactly ten thirty-thirds of a meter, that is 303.03 millimeters. It is the base length of the Japanese traditional system, close enough to the foot to be translated by it and never equal to it.
There were two shaku, and confusing them costs a quarter. The carpenter's shaku, the kanejaku, is the one above; the draper's shaku, the kujirajaku, named after the whalebone rulers it was cut from, measures 25/66 of a meter, 378.79 millimeters, exactly a quarter longer. The 1891 law kept both, the first for building and the second for cloth, so a kimono length and a beam length quoted in shaku are not the same shaku.
The shaku in other units
| 1 shaku | 0.00030303 km |
| 1 shaku | 0.30303 m |
| 1 shaku | 30.303 cm |
| 1 shaku | 303.03 mm |
| 1 shaku | 0.000188294 mi |
| 1 shaku | 0.331398 yd |
| 1 shaku | 0.994194 ft |
| 1 shaku | 11.9303 in |
| 1 shaku | 0.000163623 nmi |
| 1 shaku | 3.0303 dm |
| 1 shaku | 303,030 µm |
| 1 shaku | 0.165699 ftm |
| 1 shaku | 10 sun |
| 1 shaku | 0.166667 ken |
| 1 shaku | 0.0000771605 ri |
Frequently asked questions
How many shaku are there in a meter?
Three and three tenths exactly, so that thirty-three shaku make a round ten meters: the 1891 law tied the Japanese system to the meter through that ratio rather than the other way round. Against the foot, the shaku is 0.994194 of it, six thousandths short, and a ten foot beam measures 10.06 shaku. The gap does not show on one piece; it shows across a roof frame.
Are the Chinese chi and the Korean ja shaku?
The Korean ja is, Korea having taken up the same ten thirty-thirds of a meter. The Chinese chi is not: metrication made it a round third of a meter, 333.33 millimeters, which leaves it longer than the shaku by exactly one sun. Two drawings both marked 十尺 describe different rooms, 3.0303 meters in Japan against 3.3333 in China, thirty centimeters apart.
Why does the Japanese carpenter's square carry two scales?
Because the back of the sashigane does not measure what the front measures. The back scale, the kakume, is enlarged by the square root of two: laid across a log, it reads off the side of the largest square beam that can be cut from it, with no arithmetic. Some squares add the marume, divided by pi, which reads a diameter from a circumference. The shaku is not only a length, it is a calculating instrument, and that is what kept it alive against the meter on building sites.