The ken (間) is a traditional Japanese unit of length, equal to six Japanese feet (shaku). The exact value has varied over time and location but has generally been a little shorter than 2 meters (6 ft 7 in). It is now standardized as 1 9/11 meter. Although mostly supplanted by the metric system, this unit is a common measurement in Japanese architecture, where it is used as a proportion for the intervals between the pillars of traditional-style buildings. In this context, it is commonly translated as "bay". The length also appears in other contexts, such as the standard length of the bō staff in Japanese martial arts and the standard dimensions of the tatami mats. As these are used to cover the floors of most Japanese houses, floor surfaces are still commonly measured not in square meters but in "tatami" which are equivalent to half of a square ken.