River Rock Calculator
Find how much river rock you need for a decorative bed, dry creek bed or drainage area. Enter the area and depth to get cubic yards and tons, with a waste allowance.
River rock needed
Assumes ~1.3 tons per cubic yard; smooth rock leaves more void space than crushed stone.
How to calculate river rock
River rock is estimated like any bulk material: multiply the area in square feet by the depth in feet (depth in inches ÷ 12) to get cubic feet, then divide by 27 for cubic yards. The formula is cubic yards = area (ft²) × depth (in) ÷ 12 ÷ 27. River rock is sold by weight, and because the rounded stones pack more loosely than crushed stone, it is lighter per yard, around 1.3 US tons per cubic yard rather than the 1.4 to 1.5 tons typical of gravel and crushed stone.
Sizing a bed or dry creek
A flat decorative bed, border or mulch alternative typically uses 2 to 3 inches of river rock laid over landscape fabric. A dry creek bed, built to channel stormwater runoff, usually needs more depth, 3 to 4 inches, and is often built with a mix of stone sizes: smaller rock through the main channel and larger cobble or boulders along the edges as accents. Measure the dry creek in sections if its width varies along its length, and add the volumes together.
Stone size and coverage
Stone size changes the look, not the formula. Smaller river rock (3/4 to 1.5 inches) lays flatter and is easier to walk across, while larger cobble (2 inches and up) reads as a stronger accent but can leave more visible gaps at a shallow depth. If you are mixing sizes, estimate each size as its own area and depth, then total the tonnage.
Fabric, edging and waste
River rock is almost always installed over landscape fabric to stop weeds and keep the stone from working into the soil, and often behind steel or paver edging to keep it contained. Neither is part of this calculator's output, so budget them separately. A 5 percent waste allowance covers uneven spreading and settling. If the bed borders a lawn or planting area, the mulch calculator and topsoil calculator size those adjoining areas.