I’m sure it’s been asked before, and I’ve been scouring the boards and I’m still confused.  I also can’t find an explanation of WHAT the Rose factor is exactly, which may be the answer to my problems.

I was asked to bake a cake for 30 people. I’m used to doing 2-3 layer 9 inch cakes.

How would I convert the recipe (I have a specific one in mind for this that is not a Rose recipe this time)?
And what should I convert to - I’m thinking a 2 layer half sheet?

The Rose Factor is a method of calculating the quantity of baking powder needed for a particular pan size.  Baking powder doesn’t scale the way the other ingredients do.  It probably isn’t useful for non-Rose recipes.