Before getting deep into the weeds about yardage calculation, the first question should be: Why would a knitter want to use a different yarn other than that specified in the pattern? Several reasons come to mind:
- The specified yarn has been discontinued.
- You want to find a less expensive yarn.
- The yarn listed is a fiber to which you’re allergic or you don’t like the feel of it next to your skin.
- You’d like to see if there is a substitute yarn in your stash.
Unless allergies are an issue, a good place to start is by looking at yarn that contains the same fiber as that listed in the pattern. If the pattern calls for a fingering weight wool and you try to substitute a fingering weight silk, cotton, or bamboo, the result may be disappointing.
Next, compare yarn labels. Is the gauge on the two labels the same? Even if they are the same, the only way to know for sure is to swatch and block the substitute yarn to see if you get the same number of stitches to the inch.
After knitting and blocking a swatch of the substitute yarn, does it feel right for that pattern? If a photo accompanies the pattern, does the swatch fabric look similar to the photo?
Likely the yarn you want to substitute won’t contain the same number of yards as the yarn called for in the pattern. First, check the yardage required in your pattern. It may give a total yardage or a specific number of skeins.
Example: The pattern calls for 6 skeins and each skein contains 138 yards. So multiply 6 x 138 for a total of 828 yards.
You check the yarn label of the substitute yarn. Let’s say a skein contains 410 yards. 410 x 2 equals 820 yards—not enough for your project. You’d need more for swatching anyway so you’d purchase 3 skeins.
As with everything “knitting”, you’ll learn from each attempt at substituting yarn—both your successes and your failures. Remember an earlier post: Mistakes Are Your Friend!