||For any garment, gauge is of primary concern to the crafter. If you don't match the gauge of the pattern, your project will not be the same size as the one described in the instructions. You should always check your gauge, especially when substituting yarn.
Let's say that gorgeous cashmere sweater uses worsted weight yarn, or yarn with a CYCA classification #4. According to the CYCA, worsted yarn worked on a size 5.5 mm to 6.5 mm hook can have anywhere from 11 to 14 stitches in a four-inch swatch. That is quite a difference, when it comes to garment sizing. The bottom line is that not all worsted #4's are the same. If our cashmere is on the heavier side of worsted, you will need to seek a yarn as close to its actual weight as possible.
How do we do this without sitting in the yarn shop and swatching everything? We calculate the yarn's Wraps Per Inch (wpi). Here's how we do that.