Tatami Mats to Square Metres: How Big Is One Tatami?

Converts a number of tatami mats to square metres, using the 1.62 m² per mat defined for Japanese real-estate advertising. Real mats vary in size by region.

Explanation

Japanese rooms are still described by how many tatami mats would cover the floor: a 6-mat room, an 8-mat room. Tatami are the thick woven mats used as traditional flooring, and their standard rectangle, about twice as long as it is wide, became the yardstick for room size. Even rooms with wooden floors are advertised this way. To compare a Japanese listing with anything else, convert it to square metres.

This calculator uses 1.62 m² per mat, the figure fixed for property advertising.

S = N \times 1.62

$N$ is the number of mats and $S$ is the area in square metres.

That 1.62 m² comes from Japan's fair competition code for real-estate advertising: when a listing gives a size in mats, it must allow at least 1.62 m² per mat. It is a floor, not an exact size. A room advertised as 6 mats is therefore at least 9.72 m², and may well be more.

Example

Take the default, 6 mats.

S = 6 \times 1.62 = 9.72

A 6-mat room is 9.72 m², about 105 sq ft, or roughly 2.94 tsubo.

Notes

Real mats vary by region. A Kyoma mat, used in western Japan, is about 1.82 m²; a Chukyoma about 1.66 m²; an Edoma, the Tokyo size, about 1.55 m²; and the danchima of older apartment blocks only about 1.45 m². Six mats can therefore mean anything from about 8.7 m² to about 10.9 m² of real floor.
Two characters, 畳 and 帖, are used interchangeably for the same unit. The second is simply preferred for rooms that have no actual tatami in them.
One tsubo is loosely two mats, but at the advertising figure two mats come to 3.24 m² while a tsubo is about 3.31 m². To get tsubo from mats, convert to square metres first, then multiply by 0.3025.