Tatami 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 (IGUSA) straw.
During KAMAKURA (1192～) and MUROMACHI (1336～) periods, Tatami gradually came to be spread over whole rooms.
Tatami were originally a luxury item for the nobility. During the HEIAN period (794～), the flooring of SHINDEN-ZUKURI palatial rooms were mainly wooden, and Tatami were only used as seating for the highest aristocrats.
Nowadays Japanese houses often have very 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 (日本間) or WASHITSU (和室) “ Japanese-style room”.
Tatami are made in standard sizes, with the length exactly twice the width,
an aspect ratio of 2:1.
In Japan the size of a room is often measured by number of Tatami mats
(1 Tatami = 1 JO = 1,653 ㎡).
Alternatively, in terms of traditional Japanese area units, room area is
measured in terms of TSUBO. (1TSUBO = 2 Tatami – 3,306 ㎡)