I have a hard time figuring out how many servings in a cake, if I am doing a 18in round, 12in square, 12in round, 8in square and of course a 6in round which I can not count in the servings, how many would this cake feed? Please help. Is there a specific chart that is better to go by?

Wilton has cake preparation and servings charts by pan size and depth (per layer cake) in either (wedding) 1x2x4 or (party size) 1-1/2x2x4.

All this and more can be found in this thread...

Everything you need to know to bake, assemble and decorate tiered/stacked/layer cakes:

http://www.cakecentral.com/cake-decorating-ftopict-605188-.html

HTH