I'm doing a first bday cake for a friends daughter this weekend and told her I'd do a smash cake too. What size should the smash cake be? Not to sound cheap but since I'm doing it free, I don't want to do it too big or spend too much on it. Suggestions?
thanks
Nothing larger than 4"x4", no filling & nothing super fancy in terms of decorations 
I also usually do a 6"single layer cake with simple decorations. I charge for mine but usually have enough batter to make that and the main cake without having to make extra batter!
I charge $8 for a 6 inch round smash, but it has to accompany a larger order. Otherwise I charge $20 as that is my minimum cost just to turn on my oven and get to work! 
The smash cake I did for my baby girl was 4", 2 layers, buttercream w/fondant accents.
I did a smash cake for my friends and niece's daughter, and used a 4"cake pan. I think I've seen other people using cupcakes as a smash cake. It doesn't have to be big because it's supposed to be for the kid to do whatever the baby wants to do with it. This way, the real cake to be served to the other guests would still look nice and presentable.
4" round, torted and filled and decorated to match main cake, usually in all butter cream unless the customer requests otherwise. I figure the buttercream is easier for the little one to smash and mush and rub in their hair, which after all is the purpose of a smash cake. Oh and I only include them free with a 1st birthday, anything after that they are 12$ for a 4" round.
I do a 6" single layer decorated to match the cake and throw it in free.
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