A bride has asked me to do a 4 tier stacked cake. I had always heard you need 4" difference between tiers, but I am wondering if you can do less or if you can do less just at the top? For instance, can you do 6", 8", 12", 16" or will that look goofy? What is the size of each tier on a typical four tier cake?
Thanks for any help you can provide!

whatever you want. I do 6/8/10/12. I also do 6/9/12/15.

It depends on how many servings she's paying for. Number of servings determines the size of the tiers.

I think if the tiers are all the same shape and height, then it looks better to have the same difference between the tiers.

The only reason the 4" difference would really matter is if you've got a design element that needs a 2" ledge to sit on.

Great!!! Thank you both for you help!

If your wondering if it would be esthetically (sp??) pleasing then if you have the pans handy or some dummies in those sizes just stack them and see if you like the outcome. If you don't have them you could always go to a store that sells them and stack theirs . Other option is to see if you can find some pics (internet/magazines/books) that have those particular sized tiers and see what you think.