What tatami are
A tatami mat is a rectangular floor mat with a firm core and a woven surface. The surface is traditionally made from rush grass, called igusa, and the edges are usually bound with a strip of cloth. Cores were historically made of compressed rice straw, while many modern mats use wood-fiber boards or foam layers, which are lighter and more resistant to insects. The fresh green mat has a grassy scent that many people find pleasant, and it fades to a pale golden color over the years.
The mat is springy underfoot and slightly absorbs moisture and sound. These qualities suit a house where people sit, eat and sleep on the floor, as described in the account of floor living.
From seat to floor
In earlier periods, the word tatami referred to mats that were folded or laid down for seating, often placed on a bare wooden floor. In the Heian period, mats were set out for particular people according to rank, with thicker and more decorative ones for the most senior. Over time, particularly from the Muromachi and later periods, mats were laid across the entire floor of a room in the style of residence associated with warrior and temple society. By the Edo period, such rooms were increasingly found beyond the upper classes, though details of how quickly this happened varied by place and wealth. The timing is not precise, so these changes are best read in broad terms.
The proportions of a mat
A standard tatami is about twice as long as it is wide, so two mats side by side form a square. Its size is roughly the area one person occupies when lying down, and the traditional saying that a person needs “half a mat to sit and one mat to sleep” captures this. This relationship made it convenient to arrange mats in patterns without gaps.
The size is not identical everywhere. Regional standards differ. The mats common in the Kyoto and Kansai area tend to be larger than those in the Tokyo area, and others exist in central regions and in apartment complexes. For orientation, a common mat might measure somewhere around 1.8 meters by 0.9 meters, but a different regional or building standard can vary by a noticeable amount, so check before assuming a size. As a hypothetical example, if a mat is about 1.65 square meters, a six-mat room covers about 9.9 square meters, or roughly 10, but the real number depends on the mat standard used.
Measuring a room in mats
Because the proportions are consistent, rooms are described by the number of mats, using the counter jo. Common sizes include four and a half mats, six mats and eight mats. A six-mat room is a common bedroom or small living room, and four and a half mats is a typical size for a small room, including the compact space used for a tea gathering. Real estate listings in Japan still use this unit, usually alongside square meters, so the idea is current as well as historical.
This system worked with the structure of the house itself. Posts and beams were spaced to the size of the mats, and the sliding panels were made to fit. The modular approach means that a room, its mats and its screens fit together, an approach discussed in broader terms in studies of Japanese architecture.
Layout patterns
There are traditional ways of arranging mats. In one, called shugi-jiki, the mats are laid so that the corners of four mats do not meet at a single point, but form T-shaped junctions. This is considered suitable for celebrations. In another pattern, the four-corner meeting is allowed, and it is often associated with times of mourning or with simple arrangements. The names and customs vary, and many modern rooms follow whichever is practical. These are traditions rather than rules everyone follows, and many people are not aware of them.
Etiquette on a mat floor
Several customs follow from the nature of the mat:
- Remove shoes before stepping on it. Outdoor shoes and hard-soled slippers can damage or soil the surface, which is why the genkan entrance is such an important boundary.
- Avoid stepping on the cloth edges. The border is often a decorative strip, and in formal settings people step over it rather than on it. In a tea room, there are specific ways to walk across the mats.
- Sit with care. Heavy furniture can leave dents, so people typically place a protective mat under legs of a table or use light furniture.
Caring for the mats
Tatami do not tolerate high humidity or standing water well, and they can grow mold if kept damp. Typical care includes ventilating the room, wiping gently along the grain of the weave with a dry or slightly damp cloth and avoiding wet cleaning. Mats can be turned over, re-covered or replaced when worn. Because methods differ by mat type, it is wise to follow guidance from the maker or a qualified craftsperson when cleaning or repairing them.
More than a floor
Tatami shape how a room feels as well as how it is measured. The woven surface, the scent, the low height of the people sitting on it and the repeating rectangles give an interior its calm, regular look. Its lines of cloth border stand out like a grid and support the sense of order seen in other parts of the room, from the design of sliding screens to the placement of the display alcove. The mat is a modest object, but it quietly organizes the whole space.