Depending on how thick or thin you slice a cake, a six, eight, or ten-inch cake may not be enough or too much. Here, though, we have to go with the tradition and go for the standard measurement we use when slicing a cake. An 8-inch cake is considered the average size of a cake; depending on the cut, it can serve, at minimum, ten people and 20 people at the most. Now, if you have a smaller cake, say a six-inch cake, you can have a smaller number of people who can eat an equal portion. 8 inch cake servings