Shaku (unit)

The shaku is a traditional Japanese unit used to measure length. It is a system that originated from ancient Chinese measurement practices. Historically, the unit was based on a human hand. It measured the distance from the tip of the thumb to the tip of the forefinger. This method allowed people to measure objects using their own bodies. While the length of a shaku once varied by location, it is now a standardized measurement. It remains an important part of Japanese culture and specific trades today.

To achieve precise measurements, the shaku is divided into smaller units. One shaku is equal to ten units called sun. These sun units can be divided even further into ten smaller pieces called bu. Therefore, one shaku contains exactly 100 bu. This decimal-like system allows for very detailed work in construction and clothing.

There were different types of shaku depending on what was being measured. One version was the baleen shaku, which was used by tailors to measure cloth. These tailors used baleen, or whale whiskers, as rulers to ensure accuracy. To avoid confusion, the general version of the unit was called the ippaku. Some antique ivory rulers, known as the kyo-shaku, have even been preserved in the Shōsōin treasure house in Nara.

History shows that the shaku was not always a fixed length. In the early 19th century, most shaku were between 29 and 31 centimeters. There was also a longer version called the kinsaku. This kinsaku was 1.17 times longer than the modern value. The Meiji government eventually changed this by establishing a standard through law. Since 1891, the shaku has been standardized to a specific metric length.

Today, the shaku has a very precise definition in the metric system. One shaku is defined as 10/33 of a meter. This means a single shaku is approximately 30.3 centimeters long. If you look at a meter stick, you would find about 3.3 shaku within it. Although the Japanese government banned the use of shaku for official purposes on March 31, 1966, the unit persists. It is still a vital tool in many specialized Japanese industries.

Many cultural items and industries still rely on this measurement. Traditional Japanese carpenters use the shaku to build wooden structures. It is also essential for the construction of kimonos. A famous bamboo flute, the shakuhachi, actually derives its name from this unit. The name indicates that the flute is one shaku and eight sun in length. In the lumber trade, the shaku remains a standard for measuring wood.

The shaku also connects to other measurement systems and concepts. In the construction industry, standard sizes for plywood and drywall are based on the shaku. For example, the most common width is three shaku, which is often rounded up. In Japanese media, the term "shaku" is used to describe screen time. This refers to the amount of time a person or object appears on a screen.

Beyond Japan, the shaku has influenced other regions. The modern Taiwanese foot is based on the Japanese shaku. Additionally, the Korean Empire adopted the Japanese definition of the shaku in 1909. The system even extends into volume measurements. Ten cubic shaku is known as a koku. This was historically reckoned as the amount of rice needed to feed a peasant for one year.