The sett is the density of the warp. It is the number of ends (warp threads) per inch (epi). The sett you choose depends on the yarns, the weave structure (e.g., plain or twill, etc.) and the intended purpose of the finished piece (e.g., a loosely-woven shawl or upholstery in a tight, firm weave, or anywhere in between).It is obvious that a thin thread like sewing thread would have more threads per inch than a fat, wool yarn. See Figure 1. But how do you determine the sett considering all the factors that go into it?
 DiametersThe starting point is to evaluate the size of the yarn. This is done by laying out pieces of the yarn side-by-side, right next to one another in the space of an inch. Figure 2 shows different size yarns laid out in this way, all within one inch spaces. See that the fat yarn has 4 yarns to an inch and the thinner one has many more. 
So, we want, first of all, to know how many yarns fit into a 1-inch space. In weaving we call the yarn ends diameters. To see the diameters, look at the cut ends of the yarns as though you were looking at the cut end of a log of wood. 
Figure 3 shows a row of circles which represent the cut ends of yarns which are lying side-by-side. From this perspective, you can see that we are talking about how many diameters of the yarn fit in the one inch space. A way to find this number without cutting the yarn is to wrap the given yarn around a ruler with the yarns side-by-side, just touching. See Figure 4 below. Notice that there are 15 yarns in the inch space, and we would say then that there are 15 diameters of that yarn in one inch. 
For mixed warps: When different yarns are in the warp, find the diameters by wrapping the different yarns in the proportion they will be used. Wrap several inches. Count the number of wraps of the yarns you wound on the ruler and divide by the number of inches you wound. This gives you the average diameters per inch. |
Taken from: Weaving for Beginners and Book 1: “Winding a Warp and Using a Paddle”
According to this EPI = WPI and tat is not correct. EPI =WPI/2
This takes some thought.
She has not yet converted this to EPI for weaving, still evaluating the yarn.