For a thinner sheet cake, a 3- x 3-inch serving is usually sufficient. For a thicker sheet cake, you’ll likely want to cut 2- x 2-inch or 2- x 3-inch pieces. Once you know the size of the slices, ...

The weight of the half-sheet cake tips the scale at 9.5 pounds ... Those in the know will ask the bakery to score the right-size slices of cake ahead of time for perfect portioning.