A is a measurement in Japanese architecture. It has two principal uses:

• As a proportion for intervals between the pillars of traditional-style buildings. The word is translated in this case in English as "bay". Traditional buildings usually measure an odd number of bays, for example 3×3 or 5×5. A type of temple's gate called rōmon
  Rōmon
  The is one of two types of two-storied gate presently used in Japan . Even though it was originally developed by Buddhist architecture, it is now used at both Buddhist temples and Shinto shrines. Its otherwise normal upper story is inaccessible and therefore offers no usable space...
  
   can have dimensions going from 5×2 bays to the more common 3×2 bays down to even 1×1 bay. The Zen
  Zen
  Zen is a school of Mahāyāna Buddhism founded by the Buddhist monk Bodhidharma. The word Zen is from the Japanese pronunciation of the Chinese word Chán , which in turn is derived from the Sanskrit word dhyāna, which can be approximately translated as "meditation" or "meditative state."Zen...
  
   butsuden in the illustration measures 5×5 ken across externally because its 3×3 ken core (moya
  Moya (architecture)
  In Japanese architecture is the core of a building. Originally the central part of a residential building was called moya. After the introduction of Buddhism to Japan in the 6th century, moya has been used to denote the sacred central area of a temple building. It is generally surrounded by aisle...
  
  ) is surrounded by a 1-ken aisle called hisashi
  Hisashi (architecture)
  In Japanese architecture the term has two meanings:* As more commonly used, the term indicates the eaves of a roof, that is, the part along the edge of a roof projecting beyond the side of the building to provide protection against the weather....
  
  .

• As a length, part of the traditional system of measurement, whose value varied in history but was always around just under 2 m (6.6 ft). A ken is divided into six , each equivalent to 10 .

Although mostly supplanted by the metric system

Metric system

The metric system is an international decimalised system of measurement. France was first to adopt a metric system, in 1799, and a metric system is now the official system of measurement, used in almost every country in the world...

, this unit is still in some use in carpentry and other fields. For example, the straw mats called tatami

Tatami

A is a type of mat used as a flooring material in traditional Japanese-style rooms. Traditionally made of rice straw to form the core , with a covering of woven soft rush straw, tatami are made in standard sizes, with the length exactly twice the width...

 that cover the floors of most Japanese houses are 1-ken long and half ken wide, and floor surfaces are still measured mostly not in square meters but in tatami (as in "a six-tatami room"), and therefore indirectly in ken.

History

A building's proportions were (and, to a certain extent, still are) measured in ken, as for example in the case of Enryaku-ji

Enryaku-ji

thumb|300px|Konpon Chū-dō , Enryaku-ji's main hall is a Tendai monastery located on Mount Hiei in Ōtsu, overlooking Kyoto. It was founded during the early Heian period. The temple complex was established by Saichō , also known as Dengyō Daishi, who introduced the Tendai sect of Mahayana Buddhism...

's Konponchū-dō (Main Hall

Main Hall (Japanese Buddhism)

Main hall is the term used in English for the building within a Japanese Buddhist temple compound which enshrines the main object of veneration. Because the various denominations deliberately use different terms, this single English term translates several Japanese words, among them Butsuden,...

), which measures 11×6 bays (37.60 m × 23.92 m), of which 11×4 are dedicated to the worshipers. Inside buildings, available space was often divided in squares measuring one ken across, and each square was then called a , term written with the same Chinese character as ken. The value of a ken could change from building to building, but was usually kept constant within the same structure. There can however be exceptions. Kasuga Taisha's tiny honden

Honden

The , is the most sacred building at a Shinto shrine, intended purely for the use of the enshrined kami, usually symbolized by a mirror or sometimes by a statue. The building is normally in the rear of the shrine and closed to the general public. In front of its usually stands the haiden, or...

s dimensions, for example, are 1×1 in ken, but 1.9×2.6 in meters. In the case of Izumo Taisha

Izumo Taisha

is one of the most ancient and important Shinto shrines in Japan. No record gives the date of establishment. Located in Izumo, Shimane Prefecture, it is home to two major festivals. It is dedicated to the god Ōkuninushi , famous as the Shinto deity of marriage.A style of architecture,...

's honden, a ken is 6.32 m (20.7 ft), well above its standard value.

The distance between pillars was standardized very early and started being used as a unit of measurement. Land area in particular was measured using the ken as a basis. The unit was born out of the necessity to measure land surface to calculate taxes. At the time of Toyotomi Hideyoshi

Toyotomi Hideyoshi

was a daimyo warrior, general and politician of the Sengoku period. He unified the political factions of Japan. He succeeded his former liege lord, Oda Nobunaga, and brought an end to the Sengoku period. The period of his rule is often called the Momoyama period, named after Hideyoshi's castle...

 (16th century), the ken was about 1.97 m (6.5 ft), but around 1650 the Tokugawa shogunate

Tokugawa shogunate

The Tokugawa shogunate, also known as the and the , was a feudal regime of Japan established by Tokugawa Ieyasu and ruled by the shoguns of the Tokugawa family. This period is known as the Edo period and gets its name from the capital city, Edo, which is now called Tokyo, after the name was...

reduced it to 1.818 m (6 ft) specifically to increase taxes. After the Edo period, the ken started to be called .