Can anybody tell me how much ganache I will need to fill and ice a 2 layer 10" cake to be covered in fondant?

I'm looking at Colette Peters' recipe in her birthday cakes book, and it says that 12 oz semisweet chocolate and 8 oz heavy cream makes enough to fill and cover two 8 in cake layers. However, I'm viewing her same recipe online here:

http://www.foodandwine.com/recipes/chocolate-ganache-filling-and-glaze

and it says that 24 oz chocolate and 16 oz heavy cream makes enough for one 8 in layer cake.

So now I'm confused. Can anybody tell me how much I'll need?

I just made a 9" two layer cake yesterday and used 8 oz. of bittersweet chocolate to ice the cake in between the two layers and the outside. I used 1 cup of heavy cream and 2 tbs. butter also in the ganache. I had plenty of it for this job. Then I made another batch to pour over the top of the cake to make it really smooth.

That helps tremendously. Thank you.