Hi!
When I did a doll cake I used one half of a ball pan as the top layer, a 6in round layer, and a 7in. layer. I trimmed them down very slightly to form the dress. Depending on which serving chart you use, you can estimate the amount of servings you will get by figuring, for example, if a 6 in. layer usually gives you 6 servings, since you are only using one layer of a six in. cake, that layer will give you 3 servings. At least, that’s how I arrived at my estimations!
Since I needed more servings than what the doll cake allowed in order to remain proportional, I added a 9in. tier underneath.
Hope that helps!
Robin