Ri (Japanese) to Millimeters (ri to mm)

1 ri (Japanese) equals 3,927,272.727 millimeters (rounded).

1 ri (Japanese) = 3,927,272.727 millimeters

How to convert ri (Japanese) to millimeters

To convert ri (Japanese) to millimeters, multiply the number of ri (Japanese) by 3,927,272.727. The factor is rounded to 10 significant digits. To go the other way, multiply millimeters by 2.546296296×10⁻⁷ (rounded).

millimeters = ri (Japanese) × 3,927,272.727

Example: 10 ri (Japanese) = 39,272,727.27 millimeters.

About these units

Ri (Japanese) (ri)

JapaneseTraditional unit (still used in some regions)

36 chō, about 3.927 km. The traditional Japanese 'mile', roughly an hour's walk.

Ri comes from the Chinese li, written with characters said to combine field and earth, hinting at the span of a village. China's li has varied widely, from about 323 meters under the Tang to exactly 500 meters in the modern standard, so a bare reference to a ri is ambiguous without context.

Early Japanese practice used a ri of six cho, around 500 to 600 meters. Later it came to mean the distance a loaded porter could cover on a mountain road in an hour, which gave versions of 36, 40 and 48 cho. The Tokugawa shogunate fixed 36 cho, and the 1891 law adopted that count as 216/55 kilometer, about 3.927 kilometers or 2.44 miles.

Modern distances use kilometers, leaving the ri in proverbs and literature, where it suggests roughly an hour's walk. Because the length changed over time and by region, a distance quoted in ri from an old text should not be converted without knowing which ri was meant.

1 ri (Japanese) = 3,927.272727 meters (approximately).

Sources: Wikipedia: Ri (unit); Wikipedia: Japanese units of measurement; Japanese Wikipedia: Shakkanho (尺貫法)

Millimeter (mm)

Metric (SI)Current unit

One thousandth of a meter. Used in engineering, manufacturing and rainfall measurement.

Carl Friedrich Gauss put the millimeter at the base of his 1832 proposal for absolute units, pairing it with the milligram and the second, although the centimeter-based CGS system later won out among scientists. The name combines the metric prefix milli-, from the Latin for one thousand, with the meter. Since 1983 a millimeter has been tied to the speed of light: it is the distance light covers in 1/299,792,458,000 of a second.

Millimeters are the language of fine mechanical work. Standard rulers are divided into them, digital calipers commonly read to 0.01 mm, and mechanical pencil leads come in 0.5 and 0.7 mm. Copy paper is about 0.1 mm thick, and a thin hair, at 0.02 to 0.04 mm across, is close to the smallest thing the naked eye can see. A wave with a frequency of 300 GHz has a wavelength of 1 mm. An inch is exactly 25.4 mm. One trap for readers in the United States is that mil there traditionally means a thousandth of an inch, not a millimeter.

1 millimeter = 0.001 meters (exactly).

Sources: Wikipedia: Millimetre; Wikipedia: Centimetre-gram-second system of units; NIST Guide to the SI, Appendix B.8: conversion factors

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