Yarns Sorted by Weight Well, every time we think there's a correct way to sort yarns into groups that can be used one for another, we hit a snag. The truth is that there is so much variation in yarns that it's impossible to have absolute rules on substitutions. The Craft Yarn Council of America (CYCA) developed those handy little skeins with the numbers on them, 0 through 6, but still that isn't a complete answer for yarn substitution. There's a lot of variation among all those "4" yarns. The plain truth is you have to look at all these things, and use the infallible computer we all have (your brain!) to figure it out. Start with common sense--narrow things down first by general terms, then continue from there. You'll notice that the #3,4,&5 groups are bigger, and have more variation within them, than the thinner yarns. What
are the things that you should consider when substituting yarns? Gauge
of course, but also the fiber used, smoothness, regular or irregular
spin, indoor or outdoor use, and
the draping of it (limp to stiff). And how do you tell these things?
Sometimes it's really tough--even the color of the dye can make a
difference in how a yarn works up.