I plan to cover a half sheet in fondant - I made one batch of Rhonda's MMF and it always gives me a good size ball of fondant, but wonder if I will need two batches?

What do you think? Has anyone covered one of this size?

The terms "half sheet," "quarter sheet," and "full sheet" are misleading, as different bakeries have different definitions of how big these cakes are. I'd suggest that instead you make it a point to refer to the cake by its actual dimensions. This will avoid confusion in the case that a customer has a different definition of "half sheet" than you do. Technically, a full sheet is 18x24".

GlobalSugarArt has a great table that shows how much fondant you need for various sizes of cakes. For a 9x13" sheet cake you should plan on 3 pounds. For an 11x15" sheet cake, 4 pounds. For a 12x18" sheet cake, 5 pounds.

Hope that helps!