Ok, we have read through this forum, and seem to be even more confused. Hopefully someone can point us in the right direction. What is the industry standard for sheet cake sizes? We can't seem to find the correct combination of pan, board, and box. Any input would be greatly appreciated. 

The cake decorating industry standard is to match the cake size to the boards and boxes made.  That means a 1/4 sheet is 11 or 12 X 8 or 9; a 1/2 sheet is 12x16 or 18 and a full is two 12x16s pushed together.

If you google 'sheet cake sizes on CakeCentral' you will get the many, many threads on this subject and can read more indepth information.