Japanese Area Conversion

Like GreatBritain (from which the current U.S. system originates), Japan once had its own traditional system of area conversion, weights and measures. Since the 1920s however, Japan has turned to the metric system as its official standard for the most types of measurement. Nonetheless, the Japanese hold on to a system if area conversion calculating that dates back well over a millennium - to the Ninth Century of the Common Era (AD), in fact.
What Do Straw Mats Have To Do With It?
About the time Charlemagne was King of the Franks and the Mayan civilization was at its height in present-day Mexico and Guatemala, Japanese society - which before had been primarily rural and agricultural and centered around small villages - was undergoing tremendous change. The most significant was the rise of Buddhism, as well as increased literacy and the first written histories in the Japanese language. Partially as the result of increased centralization of government, a new standard of weights and measures - including area conversion - was necessary.
This system was known as shakkanho, from two Japanese words meaning "length" and "mass." While the shakkanho system was largely abandoned in the 1920s and finally abolished in favor of the metric system in the mid 1960s, it has remained in use in matters of real estate. The shakkanho method of area conversion calculating is based primarily on the size of the tatami, or traditional straw mats that cover the floors of Japanese homes.
The Tsubo
If you decide to rent an apartment or room in Tokyo, chances are that you'll need an area conversion calculator of some kind that is able to covert a tsubo into a square meter - or know how to do it yourself using an area conversion table. The reason for this is that property is valued by the tsubo rather than square meter or square foot.
Under the shakkanho system of measurement, the jo is the basic unit of measurement, equivalent to the size of the tatami; these are rectangular in shape. The tsubo is a unit of area conversion equal to the size of two tatamis. Real property and floor area in buildings are both measured in tsubo by Japanese real estate agents, landlords and officials who deal with land and property issues.
"Standard?"
Here's were area conversion calculating gets tricky, however; although the "traditional" size of a "standard" tatami is 90 by 180 centimeters - just shy of 1 by 2 meters - the size of tatami mats can actually vary from one region of Japan to another. A real estate or rental agency may tell you that the "standard size" of a room in a Japanese home is three tsubo, which your area conversion table may indicate as being approximately six square meters. Because the size of the tatami mat has shrunk slightly over the years, you may find your area conversion off when it comes to older buildings in different prefectures, or even cities - a six jo or three tsubo room in an older building may be substantially larger than a similar room in a new one.
An area conversion table will be of little use in determining area in Japan, but being aware of the size of tatami mats can be of help in making good estimates.