Any table with weights of butter cream (I use french) to sizes of cakes?

I have this recipe for a cake, and the recipe has also a specific recipe for french butter cream suitable to frost a 8" cake.

I want to make that cake a 3 layer 8" and a 2 layer 8"

And wondered how much frosting I had to add.

But isn't there a table for this sort of thing?

I searched but couldn't find one.

According to the buttercream recipe it creates 1lb of french butter cream (that's for 1 8" cake, no layers)