How to Measure Yarn in WPI (Wraps Per Inch)

By Claire Ortega-Reyes – 18 Comments

Yarn weight is an important factor in choosing the right yarn for crochet projects. But have you noticed that the yarns in the same weight category can have varied thicknesses? Some would deviate from the standard weight categories and describe their yarn as ‘light worsted’ or a ‘heavy dk-weight.’ So they started adding gauge information to the descriptions of weight categories, but people still encountered problems. After all, one person’s gauge is never exact; some work tightly and others loosely. And what about the unlabeled yarns we find at markets and sales? How do we know for sure what yarn weight they are?

So the yarn powers-that-be came up with the WPI (Wraps Per Inch). Everyone can use this method to check their yarn weight, and is pretty much standard if you measure properly. To do this, you will need:

  • yarn to be measured
  • ruler or measuring tape
  • pencil, pen or something similar

We simply wrap the yarn around the pencil (or in my case, marker) a few times, until it reaches about an inch in height. Make sure that the yarn is wound not too tightly nor too loosely; just enough so there are no spaces in between yarn winds. Use a flat surface while measuring the wound yarn with your ruler or tape measure.  In this example, the yarn is 11 wpi. Checking the table below, my yarn is a DK weight.

Standard Yarn Weight System Yarn Type (US) Ply (UK, NZ, AU) Wraps Per Inch (WPI)
0 or Lace Thread, Cobweb and Lace 1 – 3 ply 18+ wpi
1 or Superfine Fingering 4 ply 14 wpi
2 or Fine Sport 5 ply 12 wpi
3 or Light DK 8 ply 11 wpi
4 or Medium Worsted 10 ply 9 wpi
4 or Medium Aran 10 ply 8 wpi
5 or Bulky Bulky 12 ply 7 wpi
6 or Super Bulky Super Bulky 5-6 wpi

I hope this helps! If you have questions or comments, just leave it below I’ll get back to you soon.

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18 Comments

  1. Joanne says:

    Thanks for this information Claire! It is very helpful!!!!

  2. Brandi says:

    Thanks for this helpful information. I just came across this abbreviation in a pattern that called for 2-3 wpi in handspun yarn. Didn’t have a clue as to what was meant by this… but now I know. Thanks again!!

  3. Bananas says:

    I thought that it had to be used with a regular ruler beause of the “thickness” of it. Does it still come out the same?

  4. Lise says:

    Thank you, thank you!! I’ve been struggling with this very issue.

  5. Claire says:

    Glad I could help, Joanne, Brandi and Lise! :)

    Hello Bananas, I think it would come out about the same no matter what you use to wrap the yarn with. When you use something like rulers though, the edges may flatten the yarn instead of it lying flat on something cylindrical.So it may come out a little different, but I’m sure the difference is minute.

  6. Jhoanna says:

    Thank you so much for this Claire! I usually buy unlabeled yarns from alocal store so I find it kinda difficult to know which yarn to use for certain projects. This is so helpful! ;-)

  7. Maxine says:

    That’s great… that explains why some of my projects gauge did not match the instructions.
    Do you knit also?

  8. What about using your knitting needle or crochet hook size needed for the item to see the gauge?

  9. DawnS says:

    You’re the best! Thanx for this info…

  10. Debi Stoll says:

    I also just recently came across wpi and thought it had something to do with the number of ply that make up the strand of yarn. Thanks for the info. It’s one less thing I have to peruse.

  11. Laura says:

    So the most important thing I learned was that Aran and Worsted are two different kinds of #4 yarn. I am glad I know the truth… maybe I’ll be able to get my gauge right from now on!

  12. Claire says:

    Wow! I’m so happy to see that I’ve been able to help a lot of people. :)

    @Maxine: I don’t knit… Not yet anyway. :) It’s on my list of things to learn.
    @Sheila: You can do that, but people don’t all have the same tension while working, so the gauge people get may be different from the one specified on the yarn label. But if this has been working for you so far, stick to it. :)

  13. Debi says:

    thank you thank you thank you! I really needed this as my Christmas dress would have come out for a 5 year old rather than a 50 year old…
    ~~APPLAUSE~~

  14. I would think that using the crochet hook or knitting needles for the wpi would be great for the items people are currently making…the gauge would most likely reflect their tension as they wrap around it….the size needles from a 2 or 10 would certainly be different. Maybe a swatch to see which works best.

  15. jamie says:

    Using any object with a reasonable circumference or diameter will not affect the wpi measurement. After all, you’re measuring the length *along* the curved surface (the inch), not the lengths across the curved surface (diameter) nor around the curved surface (circumference). A different kind of surface (i.e., a flat surface that Bananas and Claire spoke of) would make a difference, but for an inch, it would be minute, as Claire mentioned (though with increases in yarn amount, the small difference might add up, but I’m unsure where this point of significance is – afghan-size maybe?).

    Also, by ‘reasonable’, I mean items such as pens, pencils (even novelty jumbo pencils!), hooks, needles, toilet paper rolls, etc. An unreasonable curved surface would be a plane fuselage, for example … way too big to wrap yarn around :P and doubtless not in any of our purses :)

    • Claire says:

      Hello Jamie! Thanks for explaining everything so clearly. Hmm… Plane fuselage… :) I sort of want to be the first person to measure wpi using that. LOL.

  16. Peggy says:

    Thank you for that very interesting test – but one important factor – shouldn’t the marker or ruller/measure tape or whatever is ued for wrapping round, be something uniform or the number of wraps would be different in each case?? Yes, I have heard of this before, but when I asked the same question, no answer was given!! Can you?

  17. Lisa says:

    Peggy and Bananas,

    I took some yarn and different tools to wrap them around, wooden ruler, marker,knitting needle,and a cassette case. Each measurement came out the same. You are measuring the width of the wrap with the yarn laying next to each other, hence wrap, not how many inches of yarn it took to make a 1 inch wrap. The only difference I got was wrapping tightly on the ruler or case and measuring on the edge where the yarn was flattened out more, but even that was a tiny difference.
    ,

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