38+44x2/40=four and one tenth 2 1/2" strips. You'll need extra to deal with t the corners and sewing together, so 5 strips is 12 1/2 inches. 3/8 of a yard is 13 1/2 inches, so that would be the perfect amount. 3/8 of a yard cut in 2 1/2 inch strips (can use 2 1/4) then folded in half will do it.
I think I used 2 1/4" last time, but I'd still buy the 3/8 yard.