I always make batthing and backing larger - I'd hate to get to the edge and not have enough of one or the other. I keep the 'leftover' backing for binding on the quilt or save it for another quilt. Works out well. The batting leftovers - well, I still need to find something to do with them - sometimes use them for table runners - as I have a whole bolt of batting and just make it big enough to make table runners...