AMy daughter requested a mad hatter topsy turvy cake for her 14th birthday this weekend. I am having a problem figuring out the diameter of each tier. I am not really worried about the number of servings, just the overall shape. This is my second attempt to make this cake and any advice would be appreciated. The first time I tried it, two yrs ago, didn't go very well. Thank you in advance.

I did this once as a two tiered cake.  The bottom tier was a 10" on top, tapering to 8" on the bottom.  The top tier was 8" on top, tapering to 6" on the bottom.  Normally I think 8" is too wide for the top of a cake but I had some dinosaurs that needed to walk around on top so it gave me the space I needed.

Here are two tutorials for a topsy turvy. There are others out there as well but these are two I have used. I found the 1st one to be a lot easier and simple but I love the 2nd one for a more dynamic, whimsical cake. GL! Post pics when you finish.

AThank you both so much for answering my question. Now have to get started baking.