How many cups of buttercream are needed for each different layer? I am making a small tiered cake for my daughter's birthday and I plan to use a 10", 8" and 6" tier all with two layers of cake.
You're right, it could be on here somewhere, but I found it on Wilton.
This Wilton chart is helpful for both batter and icing amounts for various sizes of cakes. I think an un-doctored cake mix makes about 4 1/2 cups of batter. A doctored cake will have more.
According to the Wilton yearbook (I assumed you were using rounds):
6in - 3 cups
8in - 4 cups
10in - 5 cups
It also says that it allows for top and bottom borders.
Hope this helps you!