River Rock Calculator
Calculate how much river rock you need in tons and cubic yards from area and depth.
Includes bag count and a 10 percent ordering cushion for coverage.
River rock is sold by weight, usually the ton, even though you buy it to cover an area, so the job is to turn a length, width, and depth into tons. Start with volume: multiply length by width in feet, then by the depth converted from inches to feet, which gives cubic feet. Divide by 27 for cubic yards, the unit most stone yards price against.
Turning volume into weight is where rock differs from mulch or soil. River rock is dense, running around 2,700 pounds, roughly 1.35 tons, per cubic yard, though the exact figure shifts with stone size and how wet it is. Smaller pea gravel packs tighter and weighs a little more per yard than large rounded cobbles, so treat the tonnage here as a solid estimate rather than an exact invoice figure.
Depth is the choice that most affects the total. For decorative coverage where you can still see soil between stones, 2 inches is enough. For a bed where you want full coverage and some weed suppression, go 3 to 4 inches, and remember that doubling the depth doubles the tonnage and the cost. Lay landscape fabric underneath first, because rock pushed straight onto bare soil sinks and mixes in within a season or two. Order about 10 percent extra for uneven ground and settling.