Mystery Stash Yarns: Determining Yarn Weights

It’s difficult to organize your yarn, especially when most of it has been given to you by family members cleaning out their attics. Or maybe your stash is composed of skeins you picked up from secondhand stores along with scrap yarn from old knitting or crochet projects.

Inheriting yarn and having a huge stash to choose from is great, especially for scrap yarn projects. But when you’re using these mystery bits and pieces for projects, you need to know the yarn weight in order to substitute the correct yarn, and often this information isn’t available on the yarn. It could be because the label is torn or yellowed — or maybe there’s no label at all.

Don’t worry. All is not lost! You can calculate the yarn weight with a handy little knitting secret called WPI (Wraps Per Inch).

Calculate wraps per inch - seam gauge and yarn around pencil

What you’ll need:

  • Your mystery yarn
  • A ruler
  • An object with a consistent circumference, such as a pencil

Note: It’s also an option to wrap your mystery yarn around a ruler, eliminating the need for an object with a consistent circumference. You can even buy a special WPI (wraps per inch) tool that has notches to hold the yarn in place while you wrap and comes with a handy card to help you categorize.

How to determine your yarn weight:

Begin by wrapping the yarn around the pencil. Don’t wrap too tightly. The goal is to get the yarn strands as close as possible without overlapping them or leaving holes. Usually wrapping about an inch should give you an accurate measurement, but if you’re using a yarn with a shape that isn’t consistent, like an eyelash yarn, you should wrap it for more than an inch to get the most accurate measurement possible.

Once you’ve wrapped your yarn, count the number of times you wrapped it around the pencil within the first inch.

WPI chart


WPI > 35
> 8.5 sts/inch

Treacle-Hued Yarn on Craftsy
Fyberspates Scrumptious Lace Yarn


WPI 19-22
7-8 sts/inch


WPI 15-18
5.75-6.5 sts/inch

Green Cascade Sport Yarn
Cascade Superwash Sport Yarn


WPI 12-14
5.5-6 sts/inch


WPI 9-11
4-5 sts/inch

Grey Cascade Venezia Yarn

Cascade Venezia worsted yarn 


WPI 7-8
3-3.75 sts/inch

Super Bulky

WPI < 6
1.5-3 sts/inch

So for example, if your yarn wrapped around the pencil eight times in one inch, your yarn is bulky-weight. If the yarn wrapped around the pencil 16 times in an inch, it’s a sport-weight yarn.

If you were wrapping a yarn with a funky texture as mentioned above and you wrapped extra inches, just do a little bit of math to find your WPI. If your eyelash yarn wrapped around the pencil 30 times in 2 inches, for instance, just divide 30 by 2 to find that your WPI is 15, making your eyelash yarn sport-weight.

How does WPI work?

Yarn weight is determined by the diameter of a yarn strand, right? Bulky-weight yarns work up quickly because the yarn strand is thick in diameter. Lace weights are airy because their strands are thinner. Wrapping the yarn around the pencil determines whether the yarn wraps many times around the pencil, like a lighter-weight yarn would, or the yarn doesn’t wrap as many times around the pencil, like a heavier-weight yarn would.

Don’t know what all of these different yarn weights mean? Learn all about them in our article From Lace to Bulky: Know Your Knitting Yarn Weights.

Do you have a lot of mystery yarns in your stash? Have you ever used this handy WPI technique to calculate the yarn weight?



Very helpful method for all of those mystery skeins in my stash–thanks for sharing, Ashley!


A good guide but I am confused on one point: I don’t understand how you can substitute the ruler for the pencil, as the yarn required for just one wrap is different for both, correct? Doesn’t the thickness of the pencil orruler or other object matter in the calculations?


Hi Eva! The circumference of whatever you’re wrapping the yarn around doesn’t matter because what we’re determining here is the diameter of the yarn strand. Wrap the same yarn around a ruler, a pencil, a dowel — anything with a circumference that’s consistent — and you’ll get the same wpi results for all of them. It’s the horizontal measurement that matters, not the vertical measurement. Hope that helps!


Oh, of course! (smacks forehead) That makes perfect sense now. Thanks so much for the explanation.

Debbie Winn

Great information! I’ve only been up for about an hour this morning and already I have learned something new. Thank you for sharing this. :)


love this! question…. will doing more than an inch of wrapping still work for a thick and thin (irregular diameter) type yarn?


Hey Kelly, the more you wrap an irregular diameter, the better your number. It makes it a little harder, of course, but wrapping it for several inches and taking the average is the safest bet.

Tamara Morgan

This is really handy, thanks!

However, I think it would be somewhat less confusing to not use the word “weight”. You aren’t calculating the weight, but the category of the yarn (Lace, Fingering, DK, etc). I know that these are known as ‘weights’, but when I think of weight I think of yardage per 50gm ball, for example, not the stitch count.

Which, yes, all amounts to the same thing in the end, but I thought initially you were going to teach how to actually weigh our yarn (which can also be done to determine potential gauge of a mystery yarn).

Judith Hudson

Thank you for an interesting article. How can I tell if an unlabeled yarn is acrylic or wool?


Hi, that is a great help! But does it also work with centimeters instead of inches?


Sure! You’d just need to convert the WPI chart to centimeters. The point is to make sure you wrap a large amount of yarn to get the most accurate reading.

Peg Cates

Is there a way to tell if the yarn is wool or other fibers?

Hannah Long

Thanks for the info! If the wpi is between 22 and 35, is it fingering or lace? Thanks for this handy trick!


Thank you this is really useful information but are these weights American because I think they differ from UK weights. For example I don’t know what is meant by worsted, fingering or sport.


I have the wpi tool, but it is always useful to know more than one method of doing anything. Thank you for posting this.


I’m sorry but as far as I can tell, this method is not a reliable way to determine the weight/gauge of a yarn. It’s been show in other publications (Spin Off magazine I believe) that given the same instructions, different people wrap the yarn at slightly different tensions, causing a wide variance in measurements. Most yarns are stretchy. When you say ‘Don’t wrap too tightly’, exactly how tight is that? For example, small changes in tension can cause the measurement go from 13 (DK) to 15 (Sport) WPI. Which one is it? A popular knitting magazine used to list WPI for yarns recommended in their patterns. One day I sat down and compared WPI for one specific yarn across a year’s worth of issues of the same magazine. Each issue had listed a different WPI for the same yarn! Some issues listed a WPI indicating DK, others indicated Sport. This is a neat method for getting a very rough approximation, but IMHO I’m not sure how useful it is.

Onda G

In the end it comes down to gauge. Taking the time to make a swatch is the tried and true method of knowing if a pattern will work with the yarn in stock. Our individual tensions as we crochet is just as much a variable as the tension we’d use to wrap the yarn around the ruler or pencil. It gives a rough idea, then swatch. Thanks for sharing this technique. It was explained very clearly.

Gwendoline Davina

I would like to add my thanks… Three weeks ago I discovered ‘pin weaving’, I love to weave but do not have the time or space to set up a loom so these little looms are perfect. I have not knitted for about twenty years and even then did not know any technical terms so when I read “wraps per inch” in my instructions I was completely flummoxed. Your simple explanation plus all of the above postings have really helped me to understand.
Thank you so very much xx.


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