A half-sheet cake, measuring 11 x 15 inches and made of a single layer, yields 25 to 40 servings. A half-sheet cake with two layers yields 54 party-size servings. A double-layer cake provides 74 smaller servings, which usually are offered at a wedding.
The half-sheet cake size is appropriate for most birthday parties and corporate events. A full-sheet cake feeds up to 80 people, and this size usually is reserved for large events like anniversary and graduation parties. When choosing a cake size, it is important to consider the type of event, the number of guests and the other food that is served. At a large party of adults, some guests usually decline the cake.