Tsubo, Square Meter and Tatami (Jo) Converter
＋More features: building/floor-area ratios and price per tsubo
How much can be built from the building and floor-area ratios
From the building coverage ratio (kenpeiritsu) — the share of the plot the building may cover — and the floor-area ratio (yosekiritsu) — the cap on the total floor area of all storeys — shown in a land listing, this works out the maximum building you may put on the plot.
Price per tsubo
Works out the price per tsubo and per ㎡ from the price and the area of a property.
Type one area figure and instantly see what it comes to in tsubo, square meters (㎡) and tatami mats (jo). Japanese property listings and floor plans mix all three units — a room advertised as “6畳” (6 jo) is written in ㎡ on the contract — so this is handy when you are flat-hunting in Japan and want to picture the real size.
How to use
- Enter the area you want to convert (for example 100).
- Choose the unit of that value (㎡, tsubo or jo).
- All three units appear the moment you type — no button needed.
How it is calculated
- 1 tsubo = 400/121 ㎡ ≈ 3.31 ㎡ (1 ㎡ ≈ 0.3025 tsubo)
From the definition 1 shaku = 10/33 m, one tsubo is (6 shaku)² = 400/121 ㎡. Note that the traditional shakkanho units (tsubo) are not permitted for transactions or certification under Japan's Measurement Act, so a figure in tsubo is a customary reference value. - 1 tatami mat (jo) = 1.62 ㎡
This is the standard that applies when a Japanese property advertisement states “◯ jo” (at least 1.62 ㎡ per mat, measured on a wall-center basis).
| ㎡ | Tsubo | Jo (tatami mats) |
|---|---|---|
| 9.72 | 2.94 | 6 |
| 16.2 | 4.9 | 10 |
| 33.06 | 10 | 20.41 |
| 66.12 | 20 | 40.81 |
| 100 | 30.25 | 61.73 |
Sources (primary information)
- Measurement Act (Act No. 51 of 1992) — the legal units of measurement for transactions and certification — official text, in Japanese
https://laws.e-gov.go.jp/law/404AC0000000051 (accessed July 18, 2026) - Federation of Real Estate Transaction Fair Trade Councils, “Fair Competition Code Concerning Representations of Real Estate” and its enforcement rules — the 1.62 ㎡ per tatami mat display standard — in Japanese
https://www.rftc.jp/koseikyosokiyaku/ (accessed July 18, 2026)
Assumptions and notes
- Real tatami mats differ by region and type (Kyoma about 1.82 ㎡, Chukyoma about 1.66 ㎡, Edoma about 1.55 ㎡, Danchima about 1.45 ㎡). This tool uses the single advertising standard of 1.62 ㎡.
- For the official area of a property, check the registry record and the drawings, which are stated in ㎡.
Frequently asked questions
How many tatami mats is one tsubo?
At the advertising standard of 1.62 ㎡ per mat, 1 tsubo is about 2.04 jo. The customary rule of thumb is “1 tsubo ≈ 2 tatami mats”.
Why does the same property show different areas on different documents?
Advertisements usually use the “wall-center” area measured to the middle of the walls, while the property registry uses the “inner-edge” area measured inside the walls, so the same room can show different numbers.
A “6 jo” room felt smaller than I expected. Why?
Real tatami sizes vary by region and building (Edoma and Danchima mats are smaller than Kyoma), and a listing may say “6 jo” as long as it meets the standard of 1.62 ㎡ × 6 = 9.72 ㎡ or more.