When I am figuring fabric, I start out with how much goes into one block. Say it calls for a piece to be 2 by 6 inches. That will be 12 square inches. If there are 4 of those pieces in one block and you are making 12 blocks that will be 576 square inches. So, to figure how much of that one fabric to buy, I divide 576 by 36 inches. It will take 16 inches, or get a half yard. Hope this helps you. I take a long time to figure how much fabric I need in projects, but it feels good to know that I am buying the right amount.