Units of Textile Measurement - Fabric - Ends Per Inch

Ends per inch (EPI or e.p.i.) is the number of warp threads per inch of woven fabric. In general, the higher the ends per inch, the finer the fabric is. The current fashion is to wear t-shirts with a higher thread count, such as soft and comfortable "30 single" tee shirt that has 30 threads per inch as contrasted to the standard t-shirt with an 18 thread count per inch.

Ends per inch is very commonly used by weavers who must use the number of ends per inch in order to pick the right reed to weave with. The number of ends per inch varies on the pattern to be woven and the thickness of the thread. Plain weaves generally use half the number of wraps per inch for the number of ends per inch, whereas denser weaves like a twill weave will use a higher ratio like two thirds of the number of wraps per inch. Finer threads require more threads per inch than thick ones, and thus result in a higher number of ends per inch.

The number of ends per inch in a piece of woven cloth varies depending on what stage the cloth is at. Before the cloth is woven the warp has a certain number of ends per inch, which is directly related to what size reed is being used. After weaving the number of ends per inch will increase, and it will increase again after being washed. This increase in the number of ends per inch (and picks per inch) and shrinkage in the size of the fabric is known as the take-up. The take-up is dependent on many factors, including the material and how tightly the cloth is woven. Tightly woven fabric shrinks more (and thus the number of ends per inch increases more) than loosely woven fabric, as do more elastic yarns and fibers.