I am just starting out in the cake decorating business and have my first order for a three tier topsy-turvy cake. This cake would need to serve 40 people for a little girl's first birthday party.
But how would you correctly calculate the serving size with such a cake? You use so many different size cake layers I am not sure what the actual cake serving size would be on the completed product.
Any information in this area would be greatly appreciate.
Thanks.

When I make my topsy turvy cakes, I bake one tier all the same size (no graduating sizes). Then the top layer of the tier gets cut at an angle and turned around. You'll want atleast 3 layers (6") of cake per tier to give it a good whimsy look.

As for servings, just go with how many a regular 4" cake will serve. I know there are ppl on here that normally sell 6" cakes and the servings stay the same. I would just price accordingly since you're making more cake for the look. For example, my regular 4" cakes (fondant) are $3/serving but my topsy turvy are $4/serving (more cake plus some carving if you do the whole in the tiers). Keep in mind my prices are in a rural area- you may be able to go higher depending on where you are at.