A rod is five and a half yards. To convert from square yards to square rods (why you would want to do such a ridiculous thing, I can't imagine) you divide by 30.25, which is 5.5 squared.
1 square rod = 30.25 square yards.
1 sq mile = 102400 sq rods
1 square yard = 0.03305785 square rods.
160 square rods = 1 acre.