I'm making my first wedding cake (for 100) for a friend. She wants square tiers and I've reviewed the charts for servings but I'm not sure how many tiers and what sizes I'll need since she wants to save the top tier. I'm thinking the top should be 6"?

Here is the Wilton cake serving guide.

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

So, 100 servings from a square cake (not including the top tier since the bride is saving it) would be a 12" (servings 72) and 8" (servings 32) for a total of 104 servings. So the cake will be a three tier cake 12" , 8" and 6" with the bottom two served and top saved.

I was just getting ready to say...you don't count the top tier in the serving...so, what cai311.

If she wants the cake to look proportionate (sizes equally increasing), you could use 12" x 9" x 6" squares. It would serve 72/40/18 = 112/130 (first number served and second number with total servings included).

thanks so much for the info and didn't think about using a 9" to make it look more proportional!