I have this gorgeous chunky handspun yarn and want to make a cardigan. I found a pattern that I like but the bust is 46" on 10 1/2 needles. This yarn will certainly work with size 13 (recommended). Do you think if I make the sweater with the 13s it will fit a 50" bust?
The sweater will definitely be bigger, but you'll need to do some math to figure out how much.
Knit a swatch with your yarn on the 13's and see how many stitches per inch you get. Then use that figure and divide it into the number of stitches in the sweater--back and two sides, totaled. That will give you an idea of how large the sweater will be.
For example, if you get 3 stitches per inch on the larger needles, and there are a total of 150 stitches in the sweater, then the sweater will be 50 inches around.
"Trust the pattern!"
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An easy way is to use a smaller pattern size. Taking the sts per inch you get with the 13s, multiply that by 46" - that will be how many stitches you need, front and back. See which size has close to that number of stitches around and use it.