I am making a graduation cake this weekend and I am questioning how big the cake needs to be. They would like to have a cake that serves 80 people. Would an 18x26 be enough (2x2 inch pieces)? I would use (2) 9x13's. Any advice would be greatly appreciated. This is my first cake of this size.

9x13 serves 24, so 2 would only serve 48 (by my figuring).

here is the wilton serving chart http://www.wilton.com/cakes/making-cakes/baking-party-cake-2-inch-pans.cfm although the slices are smaller that what you want, it might make it easier for you to figure out.
xx

I would use a 12 x 18 size. Maybe even two of them for 80 people, but I LOVE cake and always hope there is some to take home.

Based on the chart I use, a 2 layer 16 inch square will serve 80. (1.5x2 inch pieces)

you would need (4) 9X13's to get one 18X26".