Understanding Weaving Yarn Sizes – GIST: Yarn & Fiber
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Understanding weaving yarn sizes

Weaving yarn sizes can seem like gibberish when you’re starting out, but there is a method to the madness! First, some definitions:

ypp = the number of yards per pound. Within a specific fiber, the higher the number, the thinner the yarn. Of course, some fiber is lighter than others, so this isn’t a good measure of telling the difference in diameter between fibers.

wpi = wraps per inch. This is calculated by wrapping your yarn around one inch of a ruler, snugly but without overlapping. The number of wraps you have is your wraps per inch, which is used to calculate epi. Because everyone wraps a bit differently/more or less
snugly, there can be some variation in how two different weaver’s calculate wpi for the same yarn.

epi = ends per inch. This is how many ends of warp yarn you will have per inch of your reed. Epi is determined by the size of the yarn, the type of weaving draft you plan to use (tabby, twill, etc.), the end use of your fabric, and how heavy or drapey you would like
the end product to be ppi = picks per inch. This denotes the number of weft threads you
have per inch of woven fabric. Again, this will vary based on the size of the yarn you use, but also based on the end use of the fabric and how much drape you would like it to have.

What do all those numbers mean, for example 8/2 cotton yarn?

In simple laymen’s terms, in the US system, the lower the first number, the thicker one ply of the yarn is. The second number denotes how many plies the yarn has. To complicate matters, in other countries these numbers are sometimes reversed, but typically the smaller number is the number of plies. If you know the standard formulas for each different fiber, you can use these numbers to calculate how many yards per lb. your cone of yarn will have. If you’re interested in a fantastic and in-depth explanation of the numbering system, see Peggy Osterkamp’s blog here.

If all this still has your head swimming, don’t despair! You truly don’t have to understand the intricacies of yarn sizing to get started. Many weaving yarn shops will tell you the ypp and recommended epi and sett, so you have a jumping off point. And even if you don’t have that, once you have the yarn in hand, you can calculate the wpi to determine your epi, and you’re off to the races! 

Some final suggestions: Doing hand towels? Try 8/2 cotton or this 3-ply linen. Want to weave a warm scarf? Try fingering weight weaving wool, or alpaca. Want to weave a warm blanket? Aran weight wool is a great option.

Want to learn more about weaving yarn? Download my free 14-page guide to choosing yarn.

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