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When you're learning to weave, terms like WPI (wraps per inch), EPI (ends per inch), and weaving sett can be confusing! This blog post explains each of these common weaving terms, and explains how to calculate all three so you can start weaving with confidence.
Here are a few of the weaving terms we'll be using in this post. For a full glossary of weaving and equipment terms, check out this blog post.
WPI: wraps per inch, the number of times a yarn wraps around a 1" space on a ruler or pick-up stick.
PPI: picks per inch, the number of weft threads in one inch of woven fabric
EPI: ends per inch, the number of warp threads in one inch of woven fabric. It is often used interchangeably with sett (see below)
Sett: the distribution of warp ends in your fabric, usually over one inch (hence epi = sett).
Say you’ve just downloaded one of our weaving patterns and you have some yarn in your stash that you think will work. How do you know for sure whether or not you can substitute it? You can start by comparing the recommended sett of the project with the recommended sett of your yarn. But the label from your yarn is long gone or never had one, so now what?
Easy! Find your WPI to calculate your EPI to get your sett.
First, let’s find out the WPI of your mystery yarn. Using a ruler or smooth stick (like a pick-up stick) with markings 1” apart, wrap the yarn snugly for one inch with no space between the yarn, but make sure you aren't scrunching up or overlapping the yarn. Count how many times you wrapped the yarn in one inch. That's your WPI, or wraps per inch!
Now, if you look at your wrapped ruler or pick-up stick, the threads are butted up against each other with no space between. But to weave, your weft yarn needs space to pass over and under your warp threads.
So by definition, your WPI will always be greater than your EPI. Ok—how much greater? Generally speaking, the rule of thumb goes as follows...
Tabby, or plain weave, EPI is WPI divided by 2. So if your yarn wraps at 24 wraps per inch, you will want 12 ends per inch in your warp to give space for your weft to pass.
Twill weave EPI is about 2/3 of WPI. So if your yarn wraps at 24 wraps per inch, you will want 16 ends per inch in your warp.
These are some basic guidelines for how to determine your EPI/sett. You should use these guidelines to inform how you begin your sampling process. While everyone wants to get right into weaving, sampling is a big part of the creativity of a new weaving project, and can save you time, money and heartache by discovering what works and doesn’t work before you weave your entire project. Enjoy the sampling process!
As you set out to sample, here are a few other things to consider when deciding on your sett.
The heavier your EPI and PPI, the denser your finished fabric will be. So if, for example, you are planning a plain weave scarf and you discover that your yarn has 24 wraps per inch, your starting point for the sett would be 12 ends per inch. If you actually wanted your scarf to be light and airy, you could sample with a more open sett of 10 ends per inch, and weave your weft with a light touch so your PPI was also around 10 EPI. If, in contrast, you wanted a dense heavy placemat, you might take the same yarn and sample it at 14 or 15 EPI, with a heavy beat of 14 or 15 PPI.
As stated above, the starting point for a plain weave is typically WPI/2. The starting point for a twill weave is typically WPI * ⅔. Other weaving drafts and weaving structures will have other starting points, depending on how wide your weft floats will be and how many warp threads the weft skips over at once.
Warp-facing means that the threads, or yarns, that are most visible in the finished cloth are the warp threads, where your EPI would be significantly higher than your PPI if you are using the same yarn in warp and weft. Weft-facing means that the threads that are most visible in the finished cloth are weft threads, where your PPI would be significantly higher than your EPI if you are using the same yarn in warp and weft. A balanced weave, where both warp and weft threads are equally visible, typically has an EPI and PPI that are close to each other if you are using the same yarn in warp and weft.
Some of the most delightful accidents can happen when combining different fibers in the warp and weft. For example, a cotton yarn and a wool yarn will react very differently to wet finishing, and the woven fabric will be quite different than when it was on the loom. You’ll want to keep different shrinkage rates in mind as you sample with your yarn.
We hope you found this post helpful! If you're a new weaver and looking for other resources, be sure and check out Popular Resources for Weavers.
