How much cake will I need? Once you have chosen your style of cake, let us know how many guests you are catering for and we will ensure you have enough cake to go around. If you are catering for large numbers in addition to your main cake, an extra ‘side cake’ can be made and kept aside in the kitchen for cutting. The guide below will help you calculate how much cake you need. Portions are based on 1” slices of fruitcake and 1.2” slices of sponge cake. The bigger you slice the fewer portions you get!