WPI (Wraps Per Inch)

Explanation

WPI is a practical method for finding out which weight category an unknown yarn belongs to. You wrap the yarn closely, but without stretching it, around a ruler or a needle over one inch (2.54 cm). By counting the number of wraps, you can determine if the yarn is fingering, DK, worsted, or another thickness. This is especially useful for yarn without a label or if you want to use leftover yarn and are unsure of its thickness.