Hello!
It is not for a wedding, it is for a birthday party. Would you use 12" or 14"? I don't trust the wilton wedding size chart because it seems off to me. The cake is going to be cut by regular people, not catering staff. Thanks!

I use this for deciding how much cake to make.

http://www.earlenescakes.com/ckserchart.htm

They do list wedding cake sizes but also just rounds and squares.

HTH!

I'd do a 12" (charge 'em for the 56 servings, if applicable), and supply a printout of the cutting guide.

Thanks everyone! I ended up using Earlene's chart because I do not think a 12" will yield 56 slices. Since the cake is for a friend I told her to give me some feedback as to how many slices was she able to get out of the cake. If she tell me 56 then I will start using wilton's chart. Thanks for everything =