In order to fill the whole floor area with tatami which had previously been placed on the wooden floor to sit on, the size of tatami had to be standardized. To do this the size of the tatami and the standards of measurement used in architecture had to conform to each other. In other words, the distance between pillars used in the construction of buildings had to be standardized. So the distance between pillars was fixed as 6 shaku 5 sun (one shaku is about 30 cm and one sun is about 3 cm) and the width of a pillar 4 sun. So if two tatami were laid between pillars 12 shaku 6 sun apart, the length of one tatami would be 6 shaku 3 sun (about 190 cm). The standard size of a tatami was fixed at 6 shaku 3 sun by 3 shaku 1 sun 5 bu (one bu is about 0.3 cm, so the width of a tatami was about 94.5 cm). This was called a kyoma and its use spread throughout the Kinki (Osaka-Kyoto-Nara) area.

In the Ashikaga shoguns' Higashiyama dono (Ginkaku-ji), each room has floors of tatami. After this time, carpenters began erecting pillars so that kyoma tatami would fit exactly into the floor space. However, this technique did not spread into the Kanto (Tokyo) area. The carpenters in Tokyo insisted on measuring from the centre of one wooden pillar to the next, so that the tatami were smaller than kyoma ones, the standard being 5 shaku 8 sun (about 175cm). This was called the edoma or the inakama. In chanoyu the kyoma tatami is the standard size.