Japanese area units in a nutshell
Japanese property listings, floor plans and everyday conversation use two traditional units alongside square meters:
- Tatami (畳, also written 帖, read jō): the size of one tatami mat. Room sizes are given in mats even for Western-style rooms with wooden floors, so "洋室6帖" means a Western-style room of six mats.
- Tsubo (坪): roughly the area of two tatami mats. It is used for land, whole houses, offices and shop floors, and for prices such as "yen per tsubo".
One tsubo is defined as a square one ken (six shaku) on each side, which is exactly 400/121 m², or about 3.3058 m² and 35.58 ft². To convert roughly in your head, multiply tsubo by 3.3 for square meters, or multiply square meters by 0.3025 for tsubo. One square meter is about 10.76 square feet.
Why a tatami is not one fixed size
Unlike the tsubo, the tatami mat never had a single national size. Rooms were traditionally built to regional mat sizes, and modern apartment blocks often use smaller mats:
| Type | Mat size | One mat | Six mats | Where you find it |
|---|---|---|---|---|
| Kyōma (京間) | 191 × 95.5 cm | about 1.82 m² | about 10.9 m² (118 ft²) | Kansai, western Japan |
| Chūkyōma (中京間) | 182 × 91 cm | about 1.66 m² | about 9.9 m² | Nagoya area, parts of Tohoku and Hokuriku |
| Edoma (江戸間) | 176 × 88 cm | about 1.55 m² | about 9.3 m² (100 ft²) | Tokyo and eastern Japan |
| Danchima (団地間) | 170 × 85 cm | about 1.45 m² | about 8.7 m² (93 ft²) | Apartment blocks |
So a "six-mat room" can be anywhere from about 8.7 m² to 10.9 m², a difference of more than two square meters, or roughly the size of a single bed. When you compare flats, rely on the square-meter figure in the listing whenever it is given.
The 1.62 m² rule in property ads
For rental and sale listings, Japan's real-estate advertising code (the Fair Competition Code on the Representation of Real Estate) requires that a room described in mats has at least 1.62 m² per mat. A listing that says "LDK 10帖" should therefore have a living-dining-kitchen of at least 16.2 m², and a "6帖" bedroom at least 9.72 m², about 105 ft². That is why the calculator uses 1.62 m² as its default when you convert from tatami.
Reading 1K, 1DK and 1LDK in listings
Japanese floor plans are named by the number of rooms plus letters for the kitchen area. 1R (one room) means the kitchen is in the same room as the living space. K is a separate small kitchen, DK a dining kitchen big enough for a table, and LDK a combined living, dining and kitchen space. A "2LDK" is two bedrooms plus an LDK.
The real-estate industry's guideline says a DK should be at least 4.5 mats when there is one other room and 6 mats with two or more rooms, and an LDK at least 8 mats with one other room and 10 mats with two or more. At 1.62 m² per mat, a 10-mat LDK is about 16.2 m², or about 174 ft². The size of each room is printed on the floor plan in mats, so this converter is handy for picturing the rooms before a viewing.
Worked examples
- A typical one-room apartment of 25 m² is about 269 ft², or about 7.6 tsubo, and roughly 15 mats at the advertising standard.
- A 30-tsubo house is about 99.17 m², or 1,067 ft².
- A 70 m² family apartment is about 753 ft², or 21.2 tsubo.
- An office of 1,000 ft² back home is about 92.9 m², or 28.1 tsubo, in a Japanese listing.
Property ads usually measure floor area to the centre of the walls, while the official register for a condominium unit measures to the inside of the walls, so a flat's registered area is usually a little smaller than the advertised one. Balconies are generally not included in the floor area.
Frequently asked questions
- How many square meters is one tsubo?
- About 3.3058 m² (exactly 400/121 m²), which is about 35.58 square feet.
- How big is a 6-tatami room?
- Between about 8.7 m² and 10.9 m², depending on the mat size. In a property ad, a 6-jō room must be at least 9.72 m² (about 105 ft²).
- Is 帖 the same as 畳?
- Yes. Both are read jō and mean one tatami mat. 帖 is common for Western-style rooms with wooden floors.
- How do I convert square meters to square feet?
- Multiply by about 10.764. For example, 25 m² is about 269 ft².
Last updated: 2026-10-28