What is wpi? How do I use it to calculate sett or epi for weaving? – GIST: Yarn & Fiber
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what is wpi and how do you use it to calculate epi and sett in weaving


Wpi stands for wraps per inch of yarn, and is used to help you figure out how many ends per inch of yarn to use for your weaving warp. Calculating the wpi of your yarn is simple! All you need is the yarn, a ruler, and a smooth stick or pencil. 

  1. Measure out exactly one inch on your stick or pencil. Make two marks that show the inch, to most easily calculate the wpi of your yarn.
  2. Wrap the yarn around the stick in between the two marks that denote one inch. Wrap snugly with no space between the yarn, but make sure you aren't scrunching up or overlapping the yarn.
  3. Count how many times you wrapped the yarn in one inch.
  4. That's your wpi, or wraps per inch!

OK...so how do I use that to figure out my epi and sett? 

Epi stands for ends per inch, which means how many strands of yarn you will have in your warp in each inch. Generally speaking*, the rule of thumb is:

  • If you are doing plain tabby weave, wpi / 2 = epi. So if your yarn had 24 wraps per inch, you will want 12 ends per inch in your warp.
  • If you are doing a standard twill weave, wpi * 2/3 = epi. So if your yarn has 24 wraps per inch, you will want 16 ends per inch in your warp.

*However! This is only a basic guide to get you started with sampling. How many ends you will want per inch will depend on several things: 

  • What weaving draft do you intend to use?
  • How dense do you want your finished fabric to be?
  • Do you want it to be warp-facing (the threads most visible are the warp threads), weft-facing (the threads most visible are the weft threads), balanced (both warp and weft threads are equally visible), or somewhere in between?
  • Are you using different kinds of materials for warp and weft that will shrink in different ways when wet-finished?

The only way to get the right sett for your materials and your vision is to sample! Enjoy the sampling process, it's a big part of the creativity of creating a new weaving project. 

For more in-depth resources on calculating sett, check out Leigh's Fiber Journal, Weavolution's Weaving Sett Calculator, and the Anchorage Weaver's and Spinner's Guild Sett Chart.

Hope that is helpful! Please reach out to me with any questions, and I'll try to answer them on a future blog post.

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