Recently a colleague, who works on the knitting side of the craft, asked me what is up with Wraps Per Inch? There appears to be so much misinformation about how to use this measurement. I had such fun answering this question that I thought I’d share some of my thoughts with you.
In my mind, Wraps Per Inch (WPI) is a lousy way for a knitter to accurately measure yarn. WPI is a way to get a rough idea of where your yarn lays in the grist spectrum—say if you lost the yarn label—but its true value is to spinners and weavers.
At Spin-Off, the editors’ agree on the standard below, although there were some heated arguments before they settled on this range.
WPI matters to spinners because we have no yarn labels. Spinners need a way to quickly get a rough idea of the size of their yarn. I find the relationship between wraps and yards per pound incongruent, essentially, WPI can lie. It tells you nothing about the character of the yarn.Two yarns can have the same WPI and be radically different. One may be a tightly spun worsted yarn and the other an airy woolen yarn, but they will wrap in the space of an inch at approximately the same number. You have to use your judgment about the nature of the yarn and how you will use.
I often see knitters confusing the sett of a yarn with its WPI. The sett is the spacing if the warp ends in the heddle. You use WPI to calculate sett, but they are not one and the same. A Balanced Plain Weave (BPW) sett is half the WPI. This allows room for the weft to interlace with the warp. If you use the WPI you would get cardboard! When you see a sett expressed as a range, the middle number is the BPW number and the one to the left is for lace and the one to the right is for twill.
I find the vagaries of yarn endlessly fascinating. I know I’m in good company!