Serves and portion sizes...
When deciding on your wedding cake it pays to consider if the cake will form the dessert portion of your meal or are you serving other sweets? Also the style of event: full meal or more of a cocktail party? This will give an indication of the number of serves and also the portion size. Perhaps more important to consider is what you envision the cake to look like as you can always increase serves by having additional "kitchen cakes" - cakes kept aside and used to provide more pieces or variation in flavour.
5" cakes serve 6 dessert portions and 12 wedding portions.
7" cakes serve 8 dessert portions and 20 wedding portions.
9" cakes serve 12-16 dessert portions and 30-40 wedding portions.
11" cakes serve 16-20 dessert portions and 40-50 wedding portions.
***Amounts are conservative. Dessert portions are based on "cafe" size slices and wedding portions are based on 3cm x 3cm squares. A hot dry knife, wiped clean between each slice will ensure neat slicing.