You are confident with your math skills and I believe you have the right "formula" to do this. I don't have any suggestions to offer you. It sounds like you are on the right track. Good luck!

I agree with Donna. You're definitely on the right track. After all, instructions always say that you are supposed to use whatever needle size will give you the correct gauge because if you don't you'll end up with a finished product that is too large or too small. I knit a lot of baby blankets and most of them call for a size 6 needle and 22 stitches over 4 inches. But with a size 6 needls i get 25 stitches over 4 inches. I have to use a size 8 needle to get the (correct) gauge of 22 stitches. Otherwise, the blankets would be too narrow (it's easy to add extra pattern rows to the length of something).

So, you can either use a smaller needle or you can reduce the total number of stitches per row (just be sure to reduce evenly on both sides of the cable pattern).

First, measure across the bust of an existing tank top that fits the way you like it to fit. That is the measurement you want to go by, not your actual bust measurement. If you still think you need to make the pattern small, the others think you are on the right track, and I am terrible at math, so go for it if you still think you need to after measureing your favorite existing top.

Tami