Okay, I know that there is a lot of controversy regarding size of sheet cakes.  I am baking one this weekend for a graduation and need to make sure that it will be big enough to feed 40-50 people.  In a Wilton idea book that I have, it shows that a 12 x 18" cake double layered will feed 56.  My question to those of you that have made one, is this what you would do?  I already have 12 x 18" - 2" high pan.  Help please!!!

You need a single-layer 12" x 18" half sheet.

http://www.wilton.com/cakes/making-cakes/baking-wedding-cake-2-inch-pans.cfm
 

I use half sheet cakes (19x14) for 40-50 people, but mine are 2 layers and have filling so they are a little taller than the average half sheet or sheet cake.  When I stamp it for cutting (2x2 slices) it easily has enough piees for everyone/