The gauge of your pattern determines which weight of yarn you should select. Generally, you want to choose a yarn that is in the same weight category as the yarn recommended in your pattern [example: category 4 (also called medium/worsted/aran) or category 5 (chunky/bulky)]. For a list of the Lion Brand yarns filterable by weight, please click here. (Please note that you should also consider texture when substituting yarn; if you substitute a smooth yarn for a pattern originally in a textured yarn or vice versa, the results may look quite different.)
The best and most accurate measure for calculating amounts is yards, and all Lion Brand yarns give yardage for that reason.
First, calculate the total yardage your pattern calls for:
Example: Your pattern calls for 2 skeins of Fishermen's Wool, which are each 465 yards. The total would be 2 skeins x 465 yards = 930 yards
Next, divide the total number of yards needed for your pattern by the number of yards in each skein of your substitute yarn.
Example: Your substitute yarn is is Wool-Ease in a solid color, which has 197 yards per ball. 930 yards needed for your pattern ÷ 197 yards = 4.72 balls. You round up to 5 for the closest whole number of balls, and that is how many balls of Wool-Ease you will need to buy.
Once you have your substitute yarn, be sure to make a gauge swatch and check your gauge carefully, using whatever size hook or needle is needed to obtain the gauge of the pattern. Make sure to match the gauge in your pattern with your new yarn (adjusting hook or needle size as needed) so as to ensure that you get the right-sized finish item. Also, be sure you are satisfied with the fabric that results; it should be neither too stiff nor too loose.
NOTE: Yardage versus Weight (oz/grams) If you are working from a pattern that doesn't give yardage, you will have to rely on the weight, but, in that case, far more margine for error needs to be left. Because of different fibers and spinning techniques, there can be as much as 100 yards difference between 8 ounces of one kind of, say, worsted weight yarn, and another -- enough to really mess up a project. When you think about it, when you knit or crochet, what's going through your fingers isn't how heavy it is but how long it is.
For example, one Pound of Love is 16 ounces, 1,020 yards. To use Fishermen's Wool in a pattern calling for one Pound of Love, one would look at the yards in Fisherment's Wool: 465 each. 1,020 divided by 465 = 2.19. Each Fishermen's Wool is 8 ounces, so you can see if you just bought 2 Fishermen's Wool (to equal 16 ounces), you might well come up short, depending on whether the designer used the entire amount of Pound of Love for the design.
Finally, please note that since you are using a different yarn, your project will not look exactly the same as that pictured with the pattern.