It’s difficult to organize your yarn, especially if 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).
How does WPI work?
Yarn weight is determined by the diameter of a yarn strand? 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.
See the difference between the two yarn weights here? The first is a DK weight and the second is a super-bulky yarn.
What you’ll need
- Your mystery yarn
- A ruler
- An object with a consistent circumference, such as a pencil
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.
You can wrap the yarn around your knitting needle or crochet hook — but only if the tools has a consistent circumference. If it tapers or has an ergonomic handle, it won’t work.
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. Then, compare that number with the numbers on the WPI chart below.
WPI chart
| Yarn Weight | Wraps Per Inch | Gauge |
|---|---|---|
| 0 – Lace weight yarn | >35 | >8.5 sts/inch |
| 1 – Fingering weight yarn | 19-22 | 7-8 sts/inch |
| 2 – Sport weight yarn | 15-18 | 5.75-6.5 sts/inch |
| 3 – DK weight yarn | 12-14 | 5.5-6 sts/inch |
| 4 – Worsted weight yarn | 9-11 | 4-5 sts/inch |
| 5 – Bulky weight yarn | 7-8 | 3-3.75 sts/inch |
| 6 – Super-bulky weight yarn | <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.
Still can’t figure it out with wraps per inch? Here are two other methods you can try to determine that yarn weight.
Master Wraps Per Inch & More Yarn Essentials
Learn everything you need to know about yarn weights and fiber types to make savvy selections and achieve superb stitches.
Do you have a lot of mystery yarns in your stash? Have you ever used this handy WPI technique to calculate the yarn weight?
Editor’s Note: This post was originally published in November 2013 and was updated in February 2018.
