If you need exactly 216 inches and your fabric is 44 inches wide divide 216/44. This gives you the total number of 2.5 inch strips you need. So that comes to 4.9 (so 5) strips to meet the exact amount. If you take 5 X 2.5 = 12.5 inches of fabric. So when you add in the extras for joining strips and finishing binding I'd figure 6 strips which is 15 inches of fabric so yes 1/2 a yard would be enough. Anyone want to check me?