One of the differences between a custom bakery and a grocery store bakery are the serving sizes. Many people are used to cutting the sheet cakes from the grocery stores. These are usually 2x2x2 squares. The grocery store cakes are typically only a single layer, with no filling.
Our cakes are very different. All of our cakes include two layers of cake and a layer of filling which make our cakes just over 4 inches high. That is a tall cake! Because the cake is so much taller than a grocery store cake, you don't need a 2x2 square. Instead, you should cut a 1x2x4 piece. This not only provides you with a piece that offers the same amount of cake (8 cubic inches), but also provides for a prettier presentation on the cake plate.
Below I have provided a cutting guide. This is representative of an 8 inch round. While the pieces may not look as large as you are used to, keep in mind that they are 4 inches high.