Okay. This knit along is based on EPS, and I wrote an article about it ages go for Knitty. So, before we go further, it may be wise for you to go read it, if you haven't yet. THE ARTICLE HERE.
To repeat: I wrote the article. I still hold the copyright for everything in it because it is my creation. It is licensed to Knitty, essentially. I still hold the rights. So I'm allowed to use graphics from it, which I'm going to do. 'Cause it's mine. We can save the copyright freak-out for another more deserving occasion.
100%. Mine is 42 inches. (I'm knitting a cardigan that I want to fit over other clothes. Plus I have big boobs.) I got that by measuring a jacket that I like the fit of; armpit to armpit was 21 inches, so it's 42 inches the whole way around. Make sense, I hope?
My gauge is 5.3 stitches to the inch. Being lazy and using my lucky calculator, 5.3 x 42 = 222.6. WE WANT AN EVEN NUMBER OF STITCHES FOR THE BODY. Easy peasy. The body for me is 222 stitches.
From here you could cast on right now, or you could do ALL THE MATH at once:
If you are knitting a cardigan, you will need a steek in the front to cut open later. For the steek, add eight stitches. You need those to stabilize and cut later.
The cheat sheet:
TO FIGURE 100%: Multiply stitches per inch/cm by the circumference you want. You want an even number of stitches; it will make sense later.
TO FIGURE 90%: On your calculator, put in your 100% figure (the number of stitches, not inches or cm) then press x 90 % = on your calculator.
FOR A PULLOVER WITH RIBBING: Cast on 90%. Join and work in the round. Knit your ribbing, increase to 100% (easiest is to knit nine and make one around). Continue working in stockinette to the arm pits.
FOR A CARDIGAN WITH RIBBING: Cast on 90% plus eight stitches. (Mark the eight stitches). Join and knit in the round. Knit your ribbing, then increase to 100% plus eight stitches (easiest is to knit nine, make one around.) Work to arm pits.
FOR A PULLOVER WITH A HEM: Cast on 100% using some kind of provisional cast- on. Join and knit in the round. Use needles a size or two smaller than your main body. Knit 1.5 inches/3cm for the hem. Work one round in purl, for folding later. Shift to main needles and work body to arm pits.
FOR A CARDIGAN WITH A HEM: (This one is a little confusing. Just follow along, I'll take photos as I do mine.) Cast on 100% using some kind of provisional cast on, and smaller needles. KNIT FLAT IN STOCKINETTE (back and forth) for 1.5 inches/3cm. This is the hem. Work a row of reverse stockinette for the purl fold line. THEN, cast on eight stitches (your steek) join and knit in the round up to the arm pits. To summarize, you knit the hem flat (reduces bulk in the steek later), then cast on your eight steek stitches as a bridge between the edges and work in the round. I'll be documenting this one with photos, promise.
Questions? I bet there are questions.