Ends Per Inch in Woven Fabrics
Textile Units of Measure  Fabric  Textile Fibers  Textile Industry

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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.

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 warps 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 warps per inch.

Plain weave (also called tabby weave, linen weave or taffeta weave) is the most basic of three fundamental types of textile weaves (along with satin weave and twill). It is strong and hard-wearing, used for fashion and furnishing fabrics. In plain weave, the warp and weft are aligned so they form a simple criss-cross pattern.

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 the stage of manufacture. Before the cloth is woven, the warp has a certain number of ends per inch, which is directly related to the size reed 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.

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You may also want to learn about picks per inch which is regarding he weft yarn.  Reminder, the Ends Per Inch is regarding the "warp" yarn.