wraps per inch

Thought this may be of interest to people who weave and knit.
Wraps Per Inch vs. Gauge Swatching

Determining wraps per inch

Have you every wondered why people worry about wraps per inch (wpi)? Me too.

Some people use this method when they have two mystery yarns and they want to see if they're the same size (to use in a striped, gauge-buster vest or something like that). I can see wpi coming in handy in this sort of situation.

And spinners use the method a lot to get an idea of what weight their handspun yarn is, too. In fact, it was in the fall issue of Spin-Off magazine that I came across the article below, which got me thinking abut wraps per inch. I thought you might like to read it, too, so I've included some excerpts here.

The author is Amy Tyler, who was trained as a scientist and spent many years teaching research methods and statistics to physical therapy students. Although she now works as a fiber artist, she still finds a systematic approach to come in handy.

What is "Wraps Per Inch"?
by Amy Tyler

I was first introduced to the wraps-per-inch method of measuring of yarn thickness at a workshop in 2003. I loved the workshop, but I was skeptical of this method from the get-go. The instructions for measuring reminded me of Goldilocks and the Three Bears—not too this . . . not too that . . . just right. With just right being in the eye of the beholder.

For example, here are the instructions from the Spring 2008 issue of Spin-Off: "Wrap a length of yarn around your gauge, packing to refusal, to determine the wraps per inch (wpi) of the yarn. Packing to refusal means that you push the strands together to fill the 1-inch groove, being sure not to stretch or smoosh the yarn as you wrap it, as this will distort your result. Strands should not overlap or gap. Then simply count the number of strands in the 1-inch groove to obtain wpi."

How could a measure with such ambiguous instructions be reliable? By reliable, I mean consistent and free from error (the definition common to many research designs and methods).

I recently attended a fiber arts retreat and I had the opportunity to carry out an informal study of the reliability of wraps per inch. I asked some of the fiber folks in attendance to help me and thirteen people agreed.

I gave each person a 3-by-5-inch index card printed with ¼-inch grid marks. I folded each card in thirds to make it a bit sturdier. I then cut a notch in the card and used a pen to mark off 2 inches of the grid. I gave each person one of these cards. Then I gave the participants some basic instructions for wrapping a yarn around the card to measure wraps per inch. My instructions were essentially, "Wrap the yarn around the card, not too tight, not too loose, with wraps touching but not squished together. Wrap for 1 or 2 inches and then count the wraps in 1 inch."

I also gave each person long strands of yarn, one at a time. First, I handed out strands of Cascade 220. I asked everyone to calculate wraps per inch. When everyone had done so, I asked them to announce the measurement they'd gotten. I repeated this sequence with three more yarns: Elsebeth Lavold Silky Wool, Rowan Magpie Aran, and Schaefer Yarn Anne.

Each person got the same yarn, the same measuring tool, and the same instructions. Yet the resulting measures of wpi varied quite a bit. And in the case of Cascade's 220, no one got the published measurement; all estimates were too high. It seems that measures of the thicker yarns (such as the Magpie Aran and the 220) were more off than those of the thinner yarns. Also, not all people were consistently high or consistently low in their estimates.

I concluded that wraps per inch is not a very reliable measure.

Some spinners may find wraps per inch helpful as an approximate measure, but it shouldn't be used as the only measure of yarn thickness for a spinning project. In the end, it's not the thickness of the yarn per se that's important. It is how the yarn works in the finished product.

For knitting, there is no better way to decide if you've got the right thickness of yarn than to knit a gauge swatch. With that swatch, you can decide two very important things: Does the fabric behave as it should (drape, density, springiness)? And if you're following a pattern, are you getting the number of stitches per inch and rows per inch that you need?

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Hear, hear on the gauge issue! Yet another reason why knitters should always make a gauge swatch—we need to know what gauge we're getting with our needles and our yarn. That's really the only way to end up with a sweater that actually fits.

The Pass-Through Scarf

I know, some of you have been lucky and have winged it and ended up with a well-fitting sweater, but there are many more of you who have winged it and ended up with a sweater that you had to give away or send to the frog pond, am I right?

I hope this article has shed some light on wraps per inch for you. I know it did for me.

Cheers,