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Why gauge swatching is more important than wraps per inch

Sep 20, 2010

Determining wraps per inch

Have you ever 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 more sturdy. 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?


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.


P.S. Be sure and check out Spin-Off magazine for some really great knitting patterns, too, such as the Pass-Through Scarf by Kristi R. Schueler, shown at left. It's super cute.

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PamO@4 wrote
on Sep 26, 2010 9:37 PM

I appreciate knowing about wpi, but always considered it a weaver's tool.  I find it a bit frustrating that the yarns used in each issue of Knits are listed in the back by wpi. I thought the industry was trying to standardize yarn classification ( eg: dk is a 3).  This information, along with the guage, is more useful to a knitter, especially when trying to find a substitute yarn.

CoralS wrote
on Sep 24, 2010 2:26 PM

There is definitely a "right way" and a "wrong way" to measure WPI.  The tension in yarn can vary greatly depending on how you are wrapping it.  I am not sure if the author here looked up correct methods for doing a WPI test, but this does not look like it was done correctly.  The yarn should be SLACK and BARELY TOUCHING on each side.  Not tight and scrunched together.  WPI is very useful if done correctly.  As a recycler of thrift store sweaters, it is very useful to determine worsted weight vs. DK. vs. chunky, etc.

on Sep 22, 2010 2:08 PM

I use wpi to estimate yardage for sweaters I knit from scratch; it's great!  My wrapping tool is not flat, however.  It's a round, marked piece of dowel, which is much more reliable than wrapping yarn around a flat ruler or something.  For one, you >turn< the dowel to wrap the yarn onto it, giving more even tension.  When you wrap the yarn around with the yarn-holding hand, the tension varies from knitter to knitter.  I'm a great believer in letting the yarn do what it knows how to do--without my help!

My husband makes these tools; anyone may write to me at for more info.

LiaN wrote
on Sep 22, 2010 6:27 AM

So glad you posted these excerpts about wpi.  I find that I don't even get the same results when I do it twice.  Swatching is the best measure--and after washing and measuring you can use those swatches for coasters, finger puppets, pincushions (with a little sewing-up), cup cozies, and so on, if you don't file them and use them for future reference!  Or use one as a steek and practice picking up stitches.

diane wright wrote
on Sep 21, 2010 11:45 AM

I love all your little tutorials, but I wonder if anyone has the same problem I do with guage.  I'm always, always off.  Not just a little, but a lot.  Changing needle sizes doesn't always help because then the yarn doesn't drape right.  It is very frustrating.  Any suggestions.

KateC wrote
on Sep 20, 2010 3:01 PM


Gauge swatch is more useful for knitters, but wpi in more useful for weavers. We may sample once the warp is on the loom, but most people don't make a separate sample before threading the loom. In order to know how far apart to thread the warp, you use WPI either with a formula based on the pattern, or eyeballing it.  Once you are used to wpi it is extremely convenient for substituting yarn for any kind of project (knit/crochet/weave etc).

SandraA wrote
on Sep 20, 2010 2:02 PM

I've never seen this method of checking WPI and can see why it would lead to different results for different knitters.  I use the <a href="">WPI tool</a> from Nancy's Knit Knacks and have never had any inaccuracy problems.

jean01 wrote
on Sep 20, 2010 12:12 PM

Yes.  Excellent point and very helpful!

cacunn wrote
on Sep 20, 2010 9:47 AM

The question appeared to be using "this method when they have two mystery yarns and they want to see if they're the same size." In other words is WPI a quick method for an individual knitter to compare the size of different yarns.  This was not answered. The comparison seems to be consistency between knitters not consistency for an individual knitter.

It is highly probable that WPI will differ between individuals in the same way that a group of knitters using the same needles and yarn to knit a 4x4 gauge swatch will come up with different SPI/RPI.  

This test should be rerun by having a group of knitters find out how consistent  their WPI is on multiple sections of the same yarn.  Even if the WPI differs across the group is it close enough for each individual that the individual could use it to compare different yarns?

Could I use a 30 second WPI test to eliminate yarns and then do knit swatches for the final test?      

McKennaO wrote
on Sep 20, 2010 8:53 AM

Thank you for posting this, Kathleen. I know the process of creating swatches is tedious for newer knitters, and they tend to harbor a secret belief that if the gauge is printed on the label, it MUST be correct. MUST!

I know I'm being redundant, but everyone knits differently, and the only way to determine what sort of fabric a given yarn will create is to create a sample swatch.

Once knitting a swatch - or swatches - becomes second nature prior to commencing a project, most knitters find it to be a liberating exercise. Time is indeed saved and disappointment avoided by TAKING THE TIME TO CHECK YOUR GAUGE (Look familiar? It should. Any designer worthy of publication will incorporate this statement, or a variant thereof, at the very beginning of their designs).