River rock is heavy and round
Washed river rock runs about <strong>1.6 tons per cubic yard</strong> — heavier than crushed stone per yard and impossible to compact (round stones roll), which is why it's a decorative top dressing over fabric, not a base. Depth for landscaping coverage: 2–3 inches over weed fabric.
Buy by the ton, spread by the yard
Landscape yards sell river rock by the ton or by the bucket; the calculator's tonnage is the number to order. Budget delivery on top — rock is heavy enough that the delivery fee is real money, and wheelbarrowing two tons from the driveway is a genuine day of work.