Wraps per inch, or WPI is a way to determine the weights of any yarn.
Simply take a pencil, dowel, or ruler and mark off an inch. Then wrap the yarn around your pencil, dowel or ruler until you get to the inch mark. All that’s left is to count how many “wraps” and compare it to a yarn gauge chart.
There’s a great treatise on this method, here at Achemy Fiber Arts, as well as a chart outlining how many wraps it takes to determine different thicknesses of yarns. It’s a great way to gauge handspun yarns and other non-standard yarns.
If your family is the sort to do a turkey trot for Thanksgiving, or even just to take family pictures, you’ll want to get started knitting up some Turkey Sack Hats with this pattern from Underground Crafter.