I need to make a cake to feed about 100. I know its been discussed a 100 times but I am not good at servings. Would a 12 in. and 8 in. round staked be enough? Or a 12x18 double layer?

Here is a link you can refer to in the future. http://www.wilton.com/cakes/making-cakes/baking-wedding-cake-2-inch-pans.cfm

That's about 80 servings.

6/9/12 = 102 servings