Wraps per inch (WPI) is a unit of measurement for yarn thickness. While this word is most often used by spinners, knitters and crocheters might benefit greatly from learning it as well. It’s a common method for determining the weight of unlabeled or discarded yarn is to count the number of strands that may be laid end-to-end inside a single inch.

How to Measure Yarn Weight in WPI (Wraps per inch)?

A ruler and an object with a known diameter, such as a pencil, are required for measuring yarn in wraps per inch (WPI).

To get started, wrap a few inches of yarn around the pencil. Wraps should lie flat next to one another, with no overlap of yarn and no wide spaces in between. Avoid measuring errors by not pulling the yarn too firmly. It is recommended to practice using a yarn whose weight you are familiar with if you are uncertain of your tension.

When you have finished wrapping the yarn, you may determine the number of wraps per inch by comparing the number to the ruler’s increments. You should take measurements as you would for a gauge swatch. Compare WPI with the table given below to calculate weight of your yarn.

Remember that WPI is relative and that the outcome will change based on the yarn’s wrapping density.

How many yards of yarn do I need to make a wrap?

This formula is useful for estimating the amount of yarn needed for rectangle wraps or garter stitch projects. It excels in the medium range of yarn weights but might fail in the extremes, such as lace and super bulky. Further, it doesn’t take into consideration textured stitch patterns like cables, lace, and more.

Formula: (gauge x length x width) / 6 = yards needed. 

Here, the gauge is in stitches per inch and the Length and width are in inches.

Example: Let’s calculate the yards of Worsted yarn required for a wrap60” long and 7” wide. 

(5x60x7)/6 = 350 yards