In Japan, room size is quoted in tatami mats (jō) — a listing will say "6-tatami living room" the way an English ad might say "120 sq ft." So it surprises people that a "6-tatami" room is not one fixed size. Tatami come in four regional standards, and the physical mats in the same "6 tatami" can vary by more than 10% — about 26% between the largest and smallest standard (advertised "tatami" counts follow a separate rule, explained below). If you rent or buy in Japan, that gap is a common reason a room feels "smaller than expected." Here is how tatami, tsubo and m² relate, with the sizes in m² and sq ft.
Tsubo, tatami and m²
Japanese floor area mixes three units: tsubo, tatami (jō) and m². The tsubo is the anchor: 1 tsubo = 400/121 ≈ 3.30579 m² (about 35.6 sq ft). The odd fraction comes from defining one tsubo as one ken square, with the ken set at 20/11 m (≈1.818 m); one ken squared is (20/11)² = 400/121 ≈ 3.30579 m². As a rough rule of thumb, two tatami mats ≈ one tsubo. To move between tsubo, m² and tatami in one place, use the Tsubo / m² / Tatami converter.
Four regional tatami standards
"Two mats per tsubo" is only a guide — the actual size of a single mat depends on the region. The four common standards are:
- Kyoma — common in Kansai and western Japan; the largest.
- Chukyoma — used around Nagoya and the Tokai region; a middle size.
- Edoma — common in Kanto and eastern Japan.
- Danchima — used in apartment blocks and rentals; the smallest.
Per-standard area: 1, 6 and 8 tatami (m²)
The typical size of a single mat, and the 1-, 6- and 8-tatami areas computed from it, are:
| Standard | One mat | 1 tatami | 6 tatami | 8 tatami |
|---|---|---|---|---|
| Kyoma | 191×95.5 cm | 1.8241 m² | 10.94 m² | 14.59 m² |
| Chukyoma | 182×91 cm | 1.6562 m² | 9.94 m² | 13.25 m² |
| Edoma | 176×88 cm | 1.5488 m² | 9.29 m² | 12.39 m² |
| Danchima | 170×85 cm | 1.4450 m² | 8.67 m² | 11.56 m² |
The same "6 tatami" varies by ~26%
Floored with real mats, a 6-tatami room ranges from Kyoma's 10.94 m² down to Danchima's 8.67 m² — a difference of about 26%, roughly 1.5 mats' worth of space. Even Kyoma versus Edoma differs by about 18%. In sq ft (1 m² ≈ 10.76 sq ft) that is roughly 118 sq ft (Kyoma), 107 (Chukyoma), 100 (Edoma) and 93 (Danchima).
Note, however, that an advertised "6 tatami" (6 jō) follows a different rule from the physical mats. Japan's real-estate advertising code sets a floor of 1.62 m² per tatami (wall-centre area divided by the mat count) when a room's size is stated in mats. So an advertised "6 tatami" means at least about 9.72 m² (6 × 1.62), regardless of regional mat size. Keep "the size of the actual mats" and "the advertised tatami count" separate, and judge by the m² figure in the end.
'Kabeshin' vs 'uchinori' also change the number
Beyond the mat standard, Japanese listings have a second catch: kabeshin (wall-centre) versus uchinori (interior) area. Kabeshin measures to the centre-line of the walls; uchinori measures the usable inside of the room. For the same room, the kabeshin figure is larger. Whether an advertised m² is kabeshin or uchinori changes how much space you actually get, so don't rely on the mat count or a single m² number — check both the m² and how it was measured.
What to check before you rent or buy
- Look for an m² figure printed alongside the "N tatami" label.
- Confirm whether that m² is kabeshin or uchinori.
- To know if your furniture fits, measure in actual cm, not mat counts.
- For non-rectangular rooms, work out the real area with the Area & Volume calculator.
FAQ
Is "two mats = one tsubo" exact?
Which standard is a rental "6 tatami"?
The m² values are computed from the dimensions above. Those dimensions are typical guideline sizes for tatami layout and vary by product and property (as of 2026-07-16).