### The Indigenous Japanese System of Measurement – Shaku, Sun, Bu, and Rin

It’s not uncommon for there to be an indigenous system of measurement that is predominantly used in a given country, region, or field, even though standard systems such as metric and imperial are used on a more official or global scale.

Here in Japan, we have a measurement called the shaku, which is equivalent to 10/33 meters – about 303 millimeters, or 30.3 centimeters. The shaku can be broken down to the sun – the u pronounced like the o’s in good – which is a tenth of a shaku, about 30 millimeters.

• Note that there are variations of the shaku throughout Asia with slightly varying lengths. For example, the Chinese shaku, called chi, is equal to exactly 1/3 of a meter, or 33.33 centimeters.
• The shaku comes from the approximate or average length between nodes on bamboo.

Beyond that, the sun can be divided into a further ten, each called bu, and rin, which is a tenth of a bu. However, even though the rin is a tenth of a bu, they are only marked every 5 on most measuring tapes. In other words, there will only be one line indicating 5 rin in between each bu, instead of 9.

One bu is equal to roughly 3 millimeters. Conversion between this system and the metric system is actually quite simple and can be done in your head. For example, one shaku is equal to rougly one (shaku) times 300 millimeters – multiply the number of shaku by 300 to get the metric value.

One sun is equal to roughly one (sun) times 30 millimeters – multiply the number of sun by 30. Follow the same pattern for bu, this time multiply by 3. One (bu) times 3 equals the number of millimeters. It follows that this is not a very precise form of measurement for obvious reasons.

If you need accurate measurements, you should stick to millimeters. But many carpenters here in Japan still use shaku. Not only has it been tradition, but due to its larger increments, it’s easier to make quick ball-park measurements using shaku.

The logic behind this is that millimeters – though more accurate – takes that extra moment longer to compute due to its smaller increments, while many carpentry-related tasks often don’t require such accuracy.

Many measuring tapes, guides, rulers etc here in Japan, are made with these units, and it’s not uncommon for foreigners to mistake them for imperial units (inches) due to the similarity.

For example, many measuring tapes will have a line down the center with metric on one side and shaku units on the other. For those who don’t use shaku, this is often seen as an unnecessary feature and avoided.

But the shaku unit of measurement is an indispensable part of professional Japanese carpentry, and one that won’t be moving on anytime soon. So for those of us who plan on making a career here in Japan, familiarizing ourselves with these units – in fact, making it second nature – is important.

As a comparison, I will list the metric equivalents for the shaku, chi, and foot, respectively:

• Shaku – 0.303 meters
• Chi – 0.3333 meters
• Foot – 0.3048 meters