Gosh, as a rank, rank amatuer knitter I hesitate to post, but maybe someone hasn't heard of these tricks:
I used to knit the 2 fronts, the 2 sleeves, then do the back to finish up the yarn.
Then someone passed on:
Knit the sleeves on 4 needles to the armhole binding off. Then on 2 to form the cap.
Since I've been known to knit 2 left fronts --- grrrr -- I manipulate the pattern to do the 2 fronts and back all at once. At the armhole, I attach 2 more balls of yarn.
That way I am assured it's all the same size. Pattern mistakes -- ;-)
-- are equal, too.
Joan