Жапон стиліндегі татами төсемшесі

Straw mat used as flooring in Japan
the Japanese flooring

Tatami (畳) are types of mat used as flooring material in traditional Japanese style rooms. They are made in standard sizes, twice as long as wide, about 0.9 metres (3') by 1.8 metres (6') depending on the region. In martial arts, tatami are the floor used for training in a dojo and for competition. Tatami are covered with a weft faced weave of Juncus effusus (soft rush) (common rush), on a warp of hemp or weaker cotton. There are four warps per weft shed, two at each end (or sometimes two per shed, one at each end, to cut costs). The (core) is traditionally made from sewn together rice straw, but contemporary tatami sometimes have compressed wood chip boards or extruded polystyrene foam in their cores, instead or as well. The long sides are usually edged (縁) with brocade or plain cloth, although some tatami have no edging.

The term tatami is derived from the verb (畳む), meaning 'to fold' or 'to pile'. This indicates that the early tatami were thin and could be folded up when not used or piled in layers. Tatami were originally a luxury item for the nobility. The lower classes had mat covered earthen floors. During the Heian period, when the shinden zukuri architectural style of aristocratic residences was consummated, the flooring of shinden zukuri palatial rooms were mainly wooden, and tatami were only used as seating for the highest aristocrats. Tatami were gradually popularized and reached the homes of commoners toward the end of the 17th century. Houses built in Japan today often have few tatami floored rooms, if any. Having just one is not uncommon. The rooms having tatami flooring and other such traditional architectural features are referred to as nihonma or washitsu, "Japanese style rooms".

There are rules concerning the number of tatami mats and the layout of the tatami mats in a room. In the Edo period, "auspicious" (祝儀敷き) tatami arrangements and "inauspicious" (不祝儀敷き) tatami arrangements were distinctly differentiated, and the tatami accordingly would be rearranged depending on the occasion. In modern practice, the "auspicious" layout is ordinarily used. In this arrangement, the junctions of the tatami form a "T" shape; in the "inauspicious" arrangement, the tatami are in a grid pattern wherein the junctions form a "+" shape. It is NP complete to determine whether a large room has an auspicious arrangement using only full mats. An inauspicious layout was used to avoid bad fortune at inauspicious events, such as funerals. Now it is widely associated with bad luck and itself avoided.