How much river rock do I need?
River rock runs lighter than crushed stone, about 89 lb per cubic foot, roughly 1.2 US tons per cubic yard, because rounded stones stack with more air between them. One ton covers about 135 sq ft at 2 inches deep, 90 sq ft at 3 inches, and 65 sq ft at 4 inches. The calculator converts your area and depth into tons and yards with a waste allowance for the edges.
Match the depth to the stone size
The rule that stone yards use: the layer should be at least twice the diameter of the stone, or bare spots show through. Small 3/4 inch river rock works at 2 inches deep. Popular 1 to 3 inch rock needs 3 inches. Large 3 to 5 inch cobbles need 4 to 5 inches, which doubles the tonnage for the same area, an expensive surprise if you calculated at ground cover depth and fell in love with big stone at the yard.
Always put fabric underneath
Unlike mulch, river rock does not decompose, and unlike gravel paths, nobody rakes it flat annually. Weeds that root through rock are miserable to pull, so lay woven landscape fabric first, pinned every few feet, seams overlapped 6 inches. It also stops the rock from slowly sinking into soil, which otherwise swallows a surprising fraction of your stone within a few seasons.
Dry creek beds
A dry creek bed uses two sizes: a 4 inch bed of 1 to 3 inch river rock lining the channel, with larger 4 to 8 inch boulders placed along the banks. Calculate the channel with this page using the meander length times average width, then buy boulders individually by the piece or by weight. For actual drainage function rather than looks, size the channel with our French drain calculator logic underneath and dress the top with river rock.