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Why are traditional Japanese rooms measured by the size of floor mats?

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The main building (kondo) at Horyu-ji Temple in Ikaruga, Nara, Japan, features multi-tiered, tiled roofs and wooden architectural details on a stone base. — Japanese architecture Main building at Hōryū Temple, Ikaruga, Nara prefecture, Japan.

In traditional Japanese architecture, rooms are measured by the number of tatami mats required to cover the floor because these mats serve as a standardized modular unit for construction and design.1

A tatami mat typically measures approximately 180 by 90 cm (6 by 3 feet). Because the floor is the primary surface for sitting and sleeping in Japanese homes, the dimensions of these mats dictate the proportions of the entire interior space. For instance, architectural elements such as shoji (sliding partition doors) are designed to align with the length of the mats.12

By using the mat as a consistent unit of measurement, architects and builders ensure that the room's scale remains harmonious with the human experience, particularly from the perspective of a person seated on the floor. Consequently, the size of a room is commonly expressed by the number of mats it contains, such as a "six-mat room," which provides an immediate understanding of the space's dimensions and capacity.1