Regardless of how you spin or what equipment you use, wraps per inch (wpi) can be measured for most yarns. Wpi is meant to give a rough idea of yarn weight—not its physical weight but its category such as lace, fingering, bulky, and so on. This number, together with other details about your yarn, can help create a complete picture when describing a yarn to others or for your own future reference, but it is just one piece of the puzzle.