The ri, unit of length

The Japanese ri measures 3,927.27 meters, that is thirty-six chō or 12,960 shaku. It is the unit of the road, the distance a traveller was expected to walk in about an hour.

It is written into the landscape. In 1604 the Tokugawa government ordered ichirizuka, mounds planted with a tree, to be raised every ri along the highways from Edo, and several dozen still stand on the Nakasendō and the Tōkaidō. Do not carry the word abroad: the Korean ri is 392.7 meters, a tenth of the Japanese one, and the Chinese li has been exactly half a kilometer since the metric reform of 1929.

The ri in other units

1 ri3.92727 km
1 ri3,927 m
1 ri392,727 cm
1 ri3,927,273 mm
1 ri2.44029 mi
1 ri4,295 yd
1 ri12,885 ft
1 ri154,617 in
1 ri2.12056 nmi
1 ri39,273 dm
1 ri3,927,272,727 µm
1 ri2,147 ftm
1 ri12,960 shaku
1 ri129,600 sun
1 ri2,160 ken

Frequently asked questions

How many kilometers and miles is a ri?

3.92727 kilometers, that is 2.44029 miles. The road was reckoned in tens: ten ri, a little over 39 kilometers, was a laden traveller's day, and the fifty-three post stations of the Tōkaidō follow one another two or three ri apart, which puts a stage within half a day.

Is the kairi, the sea ri, a ri?

No, and there is nothing Japanese about it. Kairi, literally sea ri, is the Japanese name for the nautical mile, 1852 meters, less than half the land ri. Its value does not come from the traditional system but from the Earth, the nautical mile being one minute of arc of a meridian. A Japanese chart and a Japanese road map therefore use two ri in a ratio of 2.12.

Where do the 12,960 shaku of the ri come from?

From three multiplications: the ri is 36 chō, the chō 60 ken, the ken 6 shaku, and 36 times 60 times 6 is 12,960. The chō is thus 109.09 meters. Above the shaku the system counts in sixes and sixties, like a clock; below it counts in tens, the sun, the bu and the rin each splitting ten ways. The shaku is the hinge between the two.

Length