A cubic yard is 27 cubic feet, not 9 . A yard of rock , 2800lbs/2cuft = 103 or 2 bags.
How Many 50 Pound Bags Of River Rock Are Needed Per Cubic Foot?
A yard weighs about 2,800 lbs. Nine feet to a yard. 2,800/9 = 311. Six-plus bags should make a cubic foot.