My next cake is going to be a square 6/9/12 and a 2 layer 12x18 sheet cake, and I'm trying to figure out how many batches of indydebi's frosting I will have to make to fill and ice the cakes. Does anyone know how much one batch makes?

A double batch is what I usually make for a 6/9/12 inch tiered cake. I always have some left over but as far as knowing exactly how much it makes I have never measured it to see.

I never measure icing or batter by cups, either. If I need more, I make more. If I make too much, I save it until the next cake.

For wedding cakes, I tend to use four 2-lb bags of p.sugar per every 7 cake mixes. Just as a rule of thumb. Usually have good leftovers.