Tsubo, Tatami and Square Meters: Room Sizes in Japan

Why Japanese listings use three different units

Square meters are the official unit for area in Japan, and they are what you will find on registration documents, building plans and the headline area figure in most property listings. But two traditional units are still part of everyday conversation. The tsubo is mostly used for land and for prices, such as a land price quoted per tsubo, while the tatami mat, counted with the suffix jo, is used to describe the size of individual rooms.

A typical rental listing might therefore say that an apartment is 25 square meters in total, with a 7-jo Western-style room, while a house listing might give the plot as 40 tsubo. None of these units is wrong, but you need to convert them to compare properties or to plan furniture.

One tsubo is about 3.3058 square meters

The tsubo comes from the traditional shakkan-ho system of measurement. One tsubo is the area of a square measuring 6 shaku on each side, and since one shaku was fixed at 10/33 of a meter, one tsubo equals exactly 400/121 square meters, or about 3.3058 square meters. A handy reverse factor is that one square meter is about 0.3025 tsubo.

To convert, multiply tsubo by 3.3058 to get square meters, or divide square meters by 3.3058 to get tsubo. Some worked examples:

A useful rule of thumb in Japan is that one tsubo is roughly the area of two tatami mats, which is why people sometimes describe a room in both units interchangeably. As the next section shows, this is only an approximation, because tatami mats themselves are not all the same size.

• A 30-tsubo plot of land: 30 x 3.3058 = about 99.17 square meters
• A 70-square-meter condominium: 70 / 3.3058 = about 21.18 tsubo
• A 20-tsubo apartment: 20 x 3.3058 = about 66.12 square meters
• For comparison, 1 square meter is about 10.76 square feet, so 1 tsubo is about 35.6 square feet

Tatami mats are not one fixed size

Tatami were historically made to fit the rooms they were laid in, so mat sizes differ by region and by building type. Four sizes are commonly referenced. Kyoma (also called honma) is the largest and is traditionally associated with the Kansai region around Kyoto and Osaka. Chukyoma is a middle size seen around Nagoya. Edoma (also called Kantoma) is common in the Tokyo area and eastern Japan. Danchima is a smaller size often used in apartment complexes.

Because of these differences, a 6-mat room can vary noticeably in real size. Six Kyoma mats cover about 10.94 square meters, six Edoma mats about 9.29 square meters, and six Danchima mats only about 8.67 square meters. That gap of more than 2 square meters is roughly the footprint of a single bed.

• Kyoma (honma): about 191 x 95.5 cm, about 1.824 square meters
• Chukyoma: about 182 x 91 cm, about 1.656 square meters
• Edoma (Kantoma): about 176 x 88 cm, about 1.549 square meters
• Danchima: about 170 x 85 cm, about 1.445 square meters

What jo means in a real estate listing

Listings in Japan often describe Western-style rooms with wooden floors in jo as well, even though there are no tatami in them. For advertising, the real estate industry's self-regulatory code, the Fair Competition Code concerning the Representation of Real Estate, and its enforcement rules say that when room size is shown in jo, each jo should mean at least 1.62 square meters. That figure is calculated by dividing the room's area, measured to the center line of the walls, by the number of jo.

In practice this means a room advertised as 6 jo should be at least 6 x 1.62 = 9.72 square meters measured to the wall centers. Two cautions apply. First, the jo figure does not tell you which mat size would fit in the room. Second, because the measurement runs to the middle of the walls, the usable floor area inside the walls is somewhat smaller. If exact dimensions matter to you, ask the agent for a floor plan with measurements.

Room labels follow similar guidance. Under guidance issued by the national council of real estate fair trade associations, the minimums are 4.5 jo for a DK (dining-kitchen) and 8 jo for an LDK (living-dining-kitchen) in a home with one other room, rising to 6 jo for a DK and 10 jo for an LDK when there are two or more rooms. So a 1LDK and a 2LDK can both be accurate labels while describing quite different living spaces.

Reading a floor plan: a worked example

Suppose a floor plan shows a bedroom measuring 3.6 m by 2.7 m. The area is 3.6 x 2.7 = 9.72 square meters. Dividing by the 1.62 square meter listing standard gives exactly 6.0 jo. Measured in Edoma mats it would be about 6.28 mats, and in Kyoma mats about 5.33 mats, which shows how the same room can be described with different numbers depending on the reference.

For furniture planning, it is safer to work in meters than in jo. A queen-size bed, a desk and a wardrobe all have dimensions in centimeters, and the real constraints are wall lengths, door swings, windows and built-in closets, not the jo count. When you visit a property, measuring the key walls with a tape measure is still the most reliable check.

Tools that help

The area converter on this site converts between square meters, tsubo, jo, square feet, acres, hectares and several other units at once. It treats one jo as 1.62 square meters, which matches the real estate listing standard, so it is a good fit for checking advertised room sizes.

If you know a room's length and width, the rectangle area calculator gives the area, perimeter and diagonal; for a square room or a square rug, the square area calculator can also work backwards from an area to a side length. For example, a 4-square-meter square rug has sides of 2 m and a diagonal of about 2.83 m. Paste the area into the area converter to see it in tsubo, jo or square feet. All results are estimates, and official figures should always be taken from the floor plan, the property registration or an actual measurement.