When it comes to 9-inch cakes I recommend a gathering of no more. What size is a smash cake. How Much Cake To Feed 100 Google Search Cake Servings Wedding Cakes Cake Sizes According to this chart a 7 round cake feeds 15 a square feeds 24. . Keep in mind that the thinner slice of a 12 inch cake is 6 inches long and 4 or 5 inches tall. How much cake do I need for 15 guests. Unless a special half sheet pan is used the typical sheet cake baked at home measure only 13 inches by 9 inches. Cut event style a 10 inch cake can be served to as many as 39 people. How many people does a 10 inch cake feed. A half sheet cake from a bakery can measure 15 inches by 11 inches 15 12 by 10 12 or 16 by 12 inches. A 6-inch cake yields 11 portions for a round cake 18 portions for a square cake and 12 portions for a heart-shaped cake. If you are planning to serve 15 guests you should plan on making or buying at least a 7-inch cak...