Wraps Per Inch or WPI

Wraps per inch is a method of determining yarn weight. Knowing the wraps per inch helps fibre artists choose the perfect pattern for their yarn or the perfect yarn for their chosen pattern.

WPI is determined by wrapping a yarn around either a specialized Wraps Per Inch tool or around a ruler.

Too Cute Sheep WPI tool from Katrinkles 

Start by wrapping the yarn from one end evenly around the tool or ruler. Make sure not to overlap the strands so that your results are accurate. Once you have filled the space or an inch marking on a ruler count how many wraps you have.

I like using my little tool here. I find it easier to keep the yarn aligned and in place then if I were using a ruler.

I also like that it has the weights and their corresponding titles listed right there. The yarn I am measuring here is 10 WPI and is between a Worsted and DK weight.

Yarn weight can also be used to help determine needle size!