How much yarn when using a different yarn than the pattern

I am wanting to knit a sweater from a pattern that is written with a specific yarn in mind, but I plan on using a different yarn. The pattern gives the requirements as 8 skeins of 100 yards/40 grams. How do you calculate the amount of a different yarn? I assume both the yardage and weight matter, but I’m not sure what to consider.

Thanks - what a wonderful forum I’ve stumbled upon!

The yardage and the weight matter, but you need the yardage called for, you can substitute a different weight. To find out how many balls you need in the new yarn, you have to find out how many yards of the recommended yarn were called for:

#of yards in one ball of yarn called for x # of balls called for. then,

of yards in one ball of new yarn x # of balls, keep multiplying until you find out how many balls you need.

To substitute a different weight, just get the recommended gauge.

I’m close, but I’m still not quite getting it. :?? Does the weight listed in the pattern (40 grams) refer to the weight of the skein itself, or is it something else? I’m confused on how I know whether or not my new yarn is the same weight as the pattern calls for. If I can do that, then the yardage math is easy.

Yes, it refers to the weight of the skein, and it should say on the ball band what weight the yarn is, but if not, it can just be a close match.

Weight of the yarn can be figured out by looking at the st gauge and needle size on the label. Generally, if it’s with size 5-6 needles, it’s DK; size 7-8, it’s worsted; 10s, its chunky or bulky (though that’s what I use with worsted); and bigger than than is super chunky/bulky. That’s a generalization, but it’s close and fairly easy to remember.