The ken, Japanese unit of length
The ken is 1.8182 meters, exactly six shaku. It is not a tape measure unit but a module: the spacing of the pillars of a Japanese house, and the side of the square that makes one tsubo.
Two ways of using it split the country, and that is where tatami sizes come from. In the Kansai the mat goes first: the ken measures the clear span between pillars, the mat keeps 190.9 by 95.5 centimeters, and that is the kyoma. In Edo the pillar goes first: the ken is measured centre to centre, the mat loses the thickness of the timber and drops to 175.8 by 87.9, and that is the edoma. Nagoya holds the middle at 181.8 by 90.9, the chukyoma, and the post-war housing estates added the danchima, 169.7 by 84.8. A six-mat room therefore covers 10.93 square meters in Kyoto and 8.64 in post-war housing, a fifth less under the same figure carried by the advertisement.
The ken in other units
| 1 ken | 0.00181818 km |
| 1 ken | 1.81818 m |
| 1 ken | 181.818 cm |
| 1 ken | 1,818 mm |
| 1 ken | 0.00112977 mi |
| 1 ken | 1.98839 yd |
| 1 ken | 5.96516 ft |
| 1 ken | 71.582 in |
| 1 ken | 0.00098174 nmi |
| 1 ken | 18.1818 dm |
| 1 ken | 1,818,182 µm |
| 1 ken | 0.994194 ftm |
| 1 ken | 6 shaku |
| 1 ken | 60 sun |
| 1 ken | 0.000462963 ri |
Frequently asked questions
Is the ken the Japanese fathom?
The two values come close without meeting: 1.81818 meters for the ken against 1.8288 for the fathom, a centimeter apart, and the ken is 5.96516 feet. That closeness is what fixed the translation, and it is what misleads as soon as anything is measured: across a house ten ken long the gap reaches ten centimeters.
Is a thirty-three ken temple sixty meters long?
No, it is twice that. In architecture the ken stops being a length and becomes a count of bays, the space between two pillars, and that space is under no obligation to equal one ken of tape. The Sanjūsangen-dō in Kyoto, the hall of thirty-three bays, runs about 120 meters, where thirty-three measured ken would make 60. A building described in ken is counted in bays, never in meters.
Why are Kyoto houses so narrow?
Because they were taxed on their frontage, counted in ken. The maguchi, the width on the street, was the tax base, and owners pared it back and stretched the plot to the rear instead: machiya are two or three ken across the front and ten to twenty deep, which earned them the name of eel beds. Japanese property listings still quote the maguchi, often before the floor area.