With all the information reported on yarn ball bands, you may wonder why many yarns report wraps per inch (wpi). Wraps per inch can be very helpful if you have yarn without a ball band (perhaps inherited or gifted yarn). The wraps per inch will help determine the weight of the yarn. Knowing the yarn weight makes choosing a project or pattern much easier. Here’s how you measure wraps per inch.
Find an object with a consistent circumference. A knitting needle works well. You can also use a pencil or a ruler. Wrap the yarn around the object for a length of at least one inch. The yarn strands should be touching with no gaps, but should not be overlapping. Now count how many yarn strands cover 1 inch of length. Now you have wraps per inch. You may wonder why the actual circumference of the object does not matter here. Wraps per inch is measuring the width of the yarn strands. Therefore, the total length of yarn it takes to wrap the object for 1 inch will not change the wraps per inch.
In this example, I counted 10 wraps/inch. Using the wraps per inch measurement, I can figure out the weight of the yarn.
Lace weight > 35 wpi
Fingering weight: 19-22 wpi
Sport: 15-18 wpi
DK: 12-14 wpi
Worsted weight: 9-11 wpi
Bulky: 7-8 wpi
Super Bulky: < 6 wpi
I now know this yarn I inherited without a ball band is worsted weight. Now, I’m ready to pick a project!