Helpful Toolbox

Wraps Per Inch (WPI) Calculator

Wrapped an unlabeled skein around a ruler? Enter your wraps per inch and we'll tell you its yarn weight and a good needle to start with.

📖 How it works & FAQ
Enter your WPI above

What is wraps per inch?

Wraps per inch, or WPI, is a simple way to measure the thickness of a yarn without needing its original label. You wrap the strand snugly (but not stretched) around a ruler or a WPI tool, count how many wraps fit into one inch, and that number tells you the yarn's weight category. Thinner yarns pack more wraps into an inch, so a high WPI means a fine yarn; a low WPI means a thick one.

This is a lifesaver for de-stashing, thrifted skeins, hand-spun yarn, or any ball that has lost its band. Once you know the weight category, you can match it to a pattern and pick a sensible needle or hook size.

WPI to yarn weight chart

These are the common breakpoints this calculator uses: 30+ wraps is lace, 18–22 is fingering/sock, around 16 is sport, 14 is DK, 12 is worsted, 10 is aran/bulky, 8 is chunky, and 6 is super bulky. Ranges overlap a little in real life, so treat the result as a strong starting point rather than an absolute rule.

How to use it

  1. Wrap your yarn around a ruler for one full inch, laying each wrap right next to the last with no gaps and no squishing.
  2. Count the number of wraps that fit in that inch.
  3. Type that number into the WPI box above.
  4. Read your yarn weight category and the suggested needle size, then confirm with a quick gauge swatch.

FAQ

How many wraps should I count for accuracy?
Wrap at least a full inch, and ideally two inches, then divide by two. More wraps averages out any unevenness in how tightly you laid the strands.
Should I stretch the yarn while wrapping?
No. Wrap it snug but relaxed. Pulling the yarn taut thins it out and gives you a falsely high WPI.
Is the needle size exact?
It's a typical starting range for that weight. Always knit or crochet a small swatch and adjust up or down to hit your pattern's gauge.
Does everything stay on my device?
Yes. The calculation runs entirely in your browser — nothing you type is uploaded anywhere.

Results are estimates to guide yarn selection; confirm with a gauge swatch.