I've been asked to do a 1st birthday cake in a couple of weeks. The mother wants, essentially, a smash cake. I've seen people talk about it here, but never really knew what one is. Thanks to the search, I was able to find out what it is, what size people usually make it, etc. IT's been so helpful! CC is always a wealth of information.
I would say anywhere from a 4" to a 6". I wouldn't go any bigger! The elmo and cookie monster smash cakes in my pics are 6". I only made them one layer. I just made a cute little 2 layer 4" for my daughter. All white icing! I was NOT going to clean up that mess! lol