Tsubo (a unit of area in old Japanese system of weights and measures originated in China) (坪)

Tsubo is a unit of area in old Japanese system of weights and measures. Today, 1 tsubo defined the area of a square, 6 shaku (a unit of length; 1 ken [a unit of length]) on a side, which is about 3.3 square meters.

The same area of the space is also defined as bu (a unit of area)
The unit bu had been developed in China, while tsubo was later introduced as the alternative of bu unit. In general, bu unit was used for measuring the area of arable land, forest and field, while tsubo was used for the area of building sites and houses.

In ancient China during Zhou Dynasty, 'bu' (the old Japanese system of weights and measures) was established as the unit of length, specifying the length of two steps forward (by stepping forward with right leg first and left leg next, and measuring the travelled distance from the starting point to the left foot; this is a unit based on the measurement of human body parts [a anthropomorphic units]).
The 'bu' unit for measuring area was derived from that the area of a square, 1 bu on a side is also called 'bu.'
This original 1 bu area was smaller than today's 1 bu area; later 1 bu was defined as the area of 6 shaku square. During Meiji period, 1 shaku was redefined and specified as 10 over 33 meters, therefore 1 tsubo equals 10 over 33 times 6 times 2, that is, about 3.305785 square meters.

Nowadays, tsubo and bu are the base unit of the old Japanese system of weights and measures for measuring the area of a space. Units of multiples of tsubo are as follows.

Go (a unit)

1 go is equal to 0.1 tsubo.

Shaku (勺)

1 shaku is equal to 0.1 go.

Se

1 se is equal to 30 tsubo; about 99.174 square meters, therefore 1 se is roughly 1 are (a).

Tan (反 or 段)

1 tan is equal to 10 se; about 991.74 square meters (roughly 10 ares).

Cho (町 or 町歩)

1 cho is equal to 10 tan; about 9917.4 square meters (roughly 1 hectare).

Because the figures of se, tan, and cho units are close enough to the figures of 1 are, 10 ares and 1 hectare, the transition of those area units to metric system went smoothly. However, only tsubo (bu) itself could not convert into the units of the metric system by integral. Therefore, the description of the area on a registration certificate is still allowed to write in tsubo figure along with the metric figure. 1 tsubo is equal to 2 jo (tatami mat space), which is another common area units used in Japan today.

While tsubo is the Japanese origin unit, it has been also used in South Korea and Taiwan because the unit was introduced and established under the ruling of the former Empire of Japan. In case of Taiwan, the government of the Republic of China announced to switch from tsubo unit to the metric unit in 1945 for its official description of the area of a space except some governmental official documents, although the tsubo unit is still widely used in private today. In South Korea, the measurement law enacted in 1961 had officially declared to switch into the metric system; however, the usage of tsubo unit was still common in practice for real estate business, thus the government revised the measurement law in July, 2007, imposing a penalty for the usage of tsubo unit in business purpose. The area specified by tsubo unit in Taiwan and South Korea is the same as Japanese.

Other Kind of 'Tsubo' Units

There are some other kinds of 'tsubo' unit in particular fields of profession other than in the previously-mentioned real estate business.

For measuring an expensive fabric such as brocade and gold foil, or for the fields of printing and photoengraving businesses, a unique tsubo unit called sun-tsubo is used, which is defined 1 sun-tsubo as an area in 1 sun square. In case of measuring tiles and leather materials, a unique tsubo unit called shaku-tsubo is often used, which is defined 1 shaku-tsubo as an area in 1 shaku square.
A variation of the shaku-tsubo called glass-tsubo is used in the glass manufacturers and the business handling plate glasses and others, which is defined 1 glass-tsubo as 30 centimeters square (900 square centimeters)

Other than a unit for the area of a space, there is a unit used for measuring the volume of earth and sand called ryu-tsubo which is defined by the space of 6 shaku cubic.

For the paper manufacturing or printing industry, the certain weight of a paper per particular area is specified by the unit called tsubo-ryo. Original tsubo-ryo described the weight of paper per tsubo-shaku by the weight unit, monme (or momme; 3.75 grams over 0.00918 square meters equals 40.83 grams/square meters) but today's tsubo-ryo is the unit describing the weight of a paper in gram per 1 square meter, which is now called as meter tsubo-ryo or bei-tsubo.