OK, Cate… here we go! A math challenge for you, my dear!
Using LB Kitchen cotton, size 7 needles, 20 stitches cast-on for swatch
Garter Stitch - 1 yard = 39 stitches - finished size 5" (continuing to end)
Stockinett St. - 1 yrd = 36 stitches - finished size 5" (continuing to end)
2/2 front or back cross - 1 yrd = 36 stitches - finished size 3.25" (to end)
3/3 front or back cross - 1 yrd = 36 stitches - finished size 3" (to end)
4/4 front or back cross - 1 yrd = 36 stitches - finished size 2.75" (to end)
Now, I tried these numbers MANY times to verify that you get the same exact # of stitches doing cables BUT the size of the knitting gets progressively smaller. Honestly, I must have done this a dozen times just to check that I wasn’t loosing it or changing my tension to make it work or… whatever. It worked every single time to exactly 36 stitches per yard - front or back cable didn’t change it. It even worked when I had to do ‘plain’ stitches on the ends of the swatch to make the number up to 20 total stitches. Now, I did not do combination cables or braided cables - that’s gonna have to wait until tomorrow!
With what I’ve given you… what can you do with it Cate? I have had too much beer to continue this any further. I have figured out that you do not actually use more yarn to create the cables but rather that the pull of the cables decreases the overall width of your work.
This is a start in estimating yardage for cable sweaters but… I’m thinking that tomorrow is soon enough to take it to the next step. Anyone can jump in any time and help with this. Cate, I fully expect that you will be able to make some sense of this. You are, after all, Amazing Brick Girl!