re: Charging per serving: which serving size do I use???

I charge by the wedding slice, regardless of cake type. I use the industry standard cutting guides. So I go by the Wilton slice guide. If someone is asking for a 6" round cake for a small party, they will get 8 generous servings, if it’s a wedding they will get 12 servings out of the 6" round. Regardless of party type, I will charge $3.00 per serving x 12 = $36.00, this is what I sell my simple, buttercream 6" round cake for. If they want fondant or fancy decorations the price goes up from there.

You don’t need to have 2 pricing formulas, just one.