You need to know how many pieces you can get out of one cut of fabric across the width of fabric. Let's say you are cutting 10 inch squares. Assume your fabric is standard 42/44 wide. You can get 4 out of one cut across the width of fabric. so if you need 50 ten inch blocks you will need to make 13 cuts (4 x 13 = 52 so you will have 2 left over). Each of these cuts is 10 inches wide, so 13 x 10 = 130 inches, or three and three quarter yards. Same math works for any design, but first you need to figure out how many pieces you can get in one cut across the fabric.