Straw mattress in the Japanese house. A mat used as a flooring material in traditional Japanese-style rooms. In the Heian period(794-1185), tatami were used as isolated pieces and placed where necessary on top of wooden floors for sitting and sleeping. By the Muromachi period (1333-1568), the floors of some residences were covered completely with tatami. A tatami generally measures 1.9 by 0.95 meters (6.3 by 3.1 ft) in Kyoto area, 1.76 by 0.88 meters (5.8 by 2.9 ft) in Tokyo area.
The number of tatami mats is used as the standard to measure the size Japanese-style room. As for the length of the tree which is the material of the Japanese house, the dimension of the tatami mat is a standard.