We've all been there. You've found your dream crochet pattern and can't wait to get your hook started on it. It is perfect in every way except one: the yarn used. Maybe the structure is perfect but the pattern calls for acrylic, and you were looking to use a natural fiber. Or maybe it's some designer pattern that calls for a yarn that is no longer available. What's a crocheter to do? How does one go about finding a substitute yarn that will work well in the pattern?
Scenario 1: The pattern gives the yardage of yarn needed.
Lucky you! This is the easiest possible scenario in which to substitute your yarn. No math is involved in this scenario because you already know the yardage needed. However, take care to substitute with a yarn equal in thickness to the yarn used in the pattern. Note if the yarn in the pattern is worsted-weight, sport weight, fingering weight (sock yarns are fingering weight), or bulky. Sometimes the thickness of the yarn will be denoted by a number from 1-6, with 1 being the thinnest and 6 being the thickest (see more on that in our post about Yarn). If the pattern gives a brand of yarn but no thickness, a quick internet search of the brand should tell you the thickness.
Scenario 2: The pattern gives a number of skeins of yarn, but no yardage.
This scenario is common when a pattern is found on a yarn company's website, because obviously they want you to buy their yarn to make the pattern. Again, a look at the label or a quick internet search should tell you the number of yards per skein, and multiplying that by the number of skeins for the project, you can determine the total number of yards needed for the project. Whatever you do, do not go by the number of grams or ounces of yarn in the pattern. These are weight measurements, and weights can vary greatly in yarns of the same thickness. For the best accuracy, match the number of yards. Then use the tips listed above to find a suitable substitute, and buy that many yards.