In the Kyoto system (kyō-ma) fix the mat (6.3 × 3.15 shaku, about 1.91 × 0.955 m) and set the posts outside it; in the Edo system (edo-ma) fix the post grid at 6 shaku and cut the mats to fit between the posts, making them smaller.
kyō-ma ≈ 191 × 95.5 cm · chūkyō-ma ≈ 182 × 91 cm · edo-ma ≈ 176 × 88 cm
The two systems answer the old question of every modular architecture: is the module measured to the centre of the wall or to its face? In the Kyoto tatami-wari the room is the sum of its mats, so a six-mat room is the same size in any house and mats are interchangeable; in the eastern hashira-wari the structural grid comes first and the mats vary with the thickness of the posts. A “six-mat room” in Tokyo is therefore noticeably smaller than one in Kyoto.
Build the bracket set (puzuo) of blocks (dou) and arms (gong) crossing at right angles, each tier projecting no more than 30 fen beyond the one below; a set of n projecting tiers is called an (n + 3)-puzuo, from four to eight.
projection per tier ≤ 30 fen · rise per tier = 21 fen · puzuo = tiers + 3
Give a hall an odd number of bays across the front (three, five, seven, nine or eleven) so that the central axis passes through a bay and a doorway, never through a column.
Lay out the royal city as a square of nine li on each side, with three gates in each wall and, within, nine roads running north–south and nine east–west, each wide enough for nine chariots abreast.
side = 9 li · 3 gates × 4 sides · 9 jing + 9 wei · road width = 9 gui (tracks)
Find true north and south with a plumb-lined post and the shadows of sunrise and sunset, checked by the pole star; then turn the principal hall of every compound to face south.
Fix the bay (the distance between column centres) and derive every other member from it by fixed ratios: the column from the bay, the brackets and beams from the column, the rafters and their spacing from the brackets, the eaves from the rafters.
Set out the posts of a house on a square grid of one ken (six shaku, about 1.82 m) and size rooms, doors, screens and mats to fit the grid.
1 ken = 6 shaku ≈ 1.82 m · 1 tsubo = 1 ken² ≈ 3.3 m² = 2 mats
Cite this page Chris Paton, “Kyoto mats and Edo mats”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/tatami-sizes. Text, drawings and models licensed under CC BY-NC 4.0.