It depends upon how much frosting you like on a cake. If you torte the layers, it really increases the amount of frosting required. Four cups of butter (8 sticks) sounds about right for the amount of frosting I make for an 8 or 9 inch cake, but I usually have a little bit left over.
When you break it down into serving sizes, there is not really that much butter in each serving.
Sugar Sugar by SSmiley
