AI'm doing 2 Tiffany square blue Tiffany boxes. One for 10 people and one for 20 people. How much should I charge and what inch square tin should I use. Thanks in advance.

5 inch square will give you 12 wedding servings

7 inch pan will give you 24. 

That is close as I can get without being under.

I charge $4.00 per serving for this type of cake, all depends on your pricing matrix.

Hope this helps!