Japan uses Metric System and More ...
Aug
24
In addition to sum, Japan uses "TSUBO 坪" to show how large the space is. TSUBO is based on two Tatami Mat size. Two Tatami mats create a square space that is 3.3 square meters. That is 35.52 square feet.
You count each Tatami as one "jo 畳". So if the room has 6 Tatami, it is called 6 jo room. That will be 19.8 square meter or 213.13 square foot.
Now you know how Japanese explain the room size.