A layer cake is 10" x 10", and there are usually 40 in a package. If your fabric is 40" wide or more, than you should get 4 layer cakes from each 10" length of fabric. It would take just under 3 yards to cut 40 layer cakes, and 5.75 yards to cut 80. That's if you cut everything perfectly with no waste. I would buy a little extra fabric just in case.