Ordering a customized cake? It is important to note that customized cakes are not sold by weight but by size. Trying to figure out how much cake you need? Start by estimating the number of guests at your event. Typically, since not everyone takes a slice of cake, we recommend catering for about 20% less then the number of expected guests. For example, if you're expecting 100 guests, we advise catering for around 80 guests instead. You may then refer to our handy cake serving guide to estimate the size of cake you will need for your event.