100 tatami rooms — the same “six mats” can be 10.94 m² or 8.67 m²
A tatami mat is not one size. Regional standards differ and JIS lists several side by side, so “six mats” does not fix a floor area. Every meeting of 5 standards and 20 mat counts is worked out in square metres, pyeong and square feet.
6 · Floor area
- Kyōma (京間, Kansai)10.94 m² · 3.31 坪
- Rokuichima (六一間)10.27 m² · 3.11 坪
- Chūkyōma (中京間, Nagoya)9.94 m² · 3.01 坪
- Edoma (江戸間, Kantō)9.29 m² · 2.81 坪
- Danchima (団地間, flats)8.67 m² · 2.62 坪
All five standards are exactly 2:1
The long side is exactly twice the short one, because two half mats must make a whole for the floor to tile. So a mat’s area is twice the square of its short side, and that holds across every standard — only the short side changes: 955 mm for Kyōma, 910 for Chūkyōma, 850 for Danchima.
Six mats can differ by 2.27 m²
Six mats in the widest Kyōma make 10.94 m²; in the narrowest Danchima, 8.67 m². That is 26 %, and the ratio does not change with the count — the areas scale together, so it cancels. Filling a Kyōma six-mat room with Danchima mats would take 7.6 of them.
A tsubo is two mats
One tsubo is 400/121 square metres, or 3.3058 m². Two Chūkyōma mats come to 3.312 m² — within 0.2 %, which is the trace of the unit’s origin in tatami. That is why six mats are loosely called three tsubo and eight mats four; how far the shorthand drifts depends on which standard was laid.
When renting, the mat count is not enough
Two listings that both say “six mats” can differ by more than two square metres. Danchima in particular was cut down to fit apartment blocks and is smaller even than Tokyo’s Edoma. Japanese listings usually print the square metres too — that is the number to read.
A real room differs a little
These figures count only the floor the mats cover. Pillars, the built-in closet (oshiire) and thresholds have to be added or taken off. Many modern rooms also keep the mat count as a convention without laying mats at all, so a listing’s number may not describe anything physically on the floor.
Find it by standard and mat count
Floor area
Kyōma (京間, Kansai)955 × 1910 mm
Rokuichima (六一間)925 × 1850 mm
Chūkyōma (中京間, Nagoya)910 × 1820 mm
Edoma (江戸間, Kantō)880 × 1760 mm
Danchima (団地間, flats)850 × 1700 mm
How to read this
- Mat area = short side × long side. In all five standards the long side is double the short.
- Floor area = mat area × number of mats.
- At the same count, standards differ by as much as 26 %.
- One tsubo is 3.3058 m², which two Chūkyōma mats very nearly make.
Frequently asked questions
Q. How many square metres is a six-mat room?
It depends on the standard: 10.94 m² in Kyōma, 9.94 in Chūkyōma, 9.29 in Edoma, 8.67 in Danchima.
Q. Why are there several standards?
Building dimensions settled differently by region, and JIS lists them side by side. Danchima was cut later to fit apartment blocks.
Q. How much is one mat in tsubo?
It varies. A Chūkyōma mat is a little over half a tsubo, so two make roughly one.
Q. Why is a tatami 2:1?
So that two half mats make a whole one and rooms can be tiled in several patterns. All five standards hold the ratio exactly.
Q. What should I check when renting?
Read the square metres rather than the mat count — two “six-mat” rooms can differ by more than 2 m².