this is my 1st wedding cake and I'm very excited. The bride wants the 2 bottom tiers to be fake and the top 2 to be real. So I'm planing to do the following and need some real advise as I DONT want to mess this up.
I forgot to ask if she will be using the top tier to keep for her anniversary.
would just the 12" feed 40 people?
am i on the right track here?
A 12" square will feed 72. You might want to scale all your tiers down - - these are kinda big. You might go 6"-10"-14"-18". A 10" has 50 servings and I think the smaller top tier will look better. 6" is usually the norm for a top tier. This will also lower the cost for your bride - a little bit. Don't sell yourself short on pricing the dummy tiers. They need to be about 75% of the price of real cake, since you're still doing all the stacking, decorating, etc.
A 12" square serves 72.
The 2 bottom tiers don't matter as they will be fake anyway.
An 8" top tier will look pretty big. I would do 6"/8"/10"/12". The top 2 tiers which will be real cake will give you 50 servings (according to the Wilton wedding servings chart http://www.wilton.com/cakes/making-cakes/baking-wedding-cake-2-inch-pans.cfm)
If you wanted it to be bigger I would do 6"/9"/12"/15" or 16" - probably 16 as the dummies are more common.
ETA: If you are not including the top tier in the amount of servings, going with the 6/9/12/16 will give you 12 servings in the 6" and 40 servings in the 9" so you will be spot on in what they are asking of you.
Plus doing the smaller cakes will save on fondant/buttercream costs
This is a 6/8/10/12 so you can see the sizing (it's not my cake) http://cakecentral.com/gallery/1833742/white-with-plum-and-vines-wedding
and this is a 6/9/12/16 (again not my cake) http://cakecentral.com/gallery/59554/mishas-wedding-cake