What does "TSUBO" mean?

What is the commonly used "tsubo"? About the relationship between tsubo and square meters and the calculation method

When expressing the area of real estate, "tsubo" is often used. What kind of unit is this? What is the relationship between square meters and tsubo? Let's learn together with the Shaku‐kan method that is the basis of Tsubo.

What is the Shaku‐kan method?

The Shaku‐kan method  is a unit of length and area that was used before the introduction of the metric system. “里(ri)”, “町(chou)”, “間(ken)”, “丈(jou)”, “尺(shaku)”, and “寸(sun)” represent length and distance, “反”(tan), “畝(se)” and “坪(tsubo)” represent area and land area, "石(koku)", "斗(to)", "升(shou)", "合(gou)", "勺(shaku)" are used to express the volume, and "貫(kan)", "斤(kin)", "両(ryou)" and "匁(monme)" are used to represent the weight. However, the use of the Shaku‐kan method is prohibited in general commercial transactions from 1959, and the display of land and buildings was abolished in 1966. After that, if we use the Shaku‐kan method for "transaction or proof", we will be fined, but it is still customary in some industries.
In real estate, “坪(tsubo)” is often used for the area of land and buildings, and the building area is also called “建坪(tate tsubo)”. In addition, the units of length, "間(ken)" and "尺(shaku)", are often used. Looking at old real estate registry, "反(tan)" and "畝(se)" often appear. Other than real estate, there are many opportunities to hear the units such as "升(shou)" and "合(gou)" of sake, and "寸(sun)" such as nail length.

Relationship between tsubo and square meter

One tsubo is about 3.30578 square meters and one square meter is about 0.3025 tsubo. In reality, the fraction continues endlessly, but it is not practical to make it smaller. For example, when converting 100 square meters to tsubo, divide 100 by 3.30578 to get 30.25 tsubo, or multiply 100 by 0.3025 to get 30.25 tsubo. This "tsubo" is often written as 3.3 square meters, but when calculated with 3.3, an error of about 0.05 square meters will occur for 100 square meters. Although it is a slight difference, it can be a big difference in the amount of money in metropolitan areas with high land prices.
As a general rule, the real estate sales contract does not show the tsubo, but when the tsubo is used in advertisements and pamphlets, it will be shown in brackets after the area in square meters. However, in the contract of the actual sale and purchase of land (a contract method in which the purchase price is settled according to the actual measurement result of the site), the unit price may be displayed as "Tsubo unit price". In this case, if you do not clarify whether the conversion of the tsubo is 3.3 square meters or 3.30578 square meters, it may cause unexpected trouble to be careful.

The relationship between 坪(tsubo), 間(ken), and 尺(shaku), and the size of the Tatami mat

One 尺(shaku) is about 0.303030 meters, and one 間(ken) is about 6 尺(shaku) and is about 1.818182 meters. A square on one 間(ken) is one tsubo, and the square of about 1.818182 is about 3.30578. The 間(ken) is often used as a unit of length of architecture, and is about 1.8 meters for one 間(ken) (6 尺(shaku)) or about 90 cm for a 半間(han ken, half of ken) is often the standard size for fittings. On the other hand, recently, the standard size is 1 meter, which is called "meter module". Before the Building Standard Act came into effect in 1950, the 間(ken) was used as the standard for road width. For this reason, old roads often have widths of 2 間(ken) (about 3.6 meters) and 1 間(ken) 3尺(shaku)(about 2.7 meters), which "setback" is required to match the current standard of 4 meters. 
The size of 1 坪(tsubo) is said to be 2 tatami mats, but the size of tatami mats varies from region to region, and 2 tatami mats are exactly 1坪(tsubo) of 中京間(Chukyo-ma/Nagoya-size tatami mat). This is also called 三六間 (Saburokuma), and each piece is 3 尺(shaku) × 6 尺(shaku). The 2 tatami mats of 京間 (Kyoma/Kyoto-size tatami mat) (Honma/official size of a tatami mat for measuring room size) are larger than 1 坪(tsubo), while the 2 tatami mats of 江戸間(Edo-ma/Kanto-size tatami mat) (Kanto-ma) are smaller than 1 tsubo. ​The size of the so-called housing complex is smaller than the 江戸間(Edo-ma), and even if two of them are lined up, it is only about 0.87 tsubo.

Today, we explained about 坪(tsubo), which is used to describe size of real estate, and the size of tatami mats. All of them are unique to Japan and are not used often, but please understand for reference.