adjusting a sweater pattern size?
I want to make a cute sweater from "The yarn girls guide to kid knits", but the sizes given only go up to 3 year. I want to make this for a 5 year old. My problem is that the increases for each size don't seem all even... for example, it says cast on 40 (44, 48, 54, 60) stitches. ... .... work until piece measures 3" (3 1/2, 3 3/4, 4 1/2, 5").
Is there a mathmatical figure to adding up two sizes from what I've given above, that can be applied to the whole pattern?
Thanks for any and all help!!