How this instrument works
River rock is naturally rounded, water-worn stone — smooth, spheroidal pebbles shaped by tumbling in moving water over time — widely used decoratively in landscaping for dry creek beds, garden borders, and ground cover, distinct from the sharp-edged, angular look of crushed aggregate. Its rounded shape and typically larger, more variable size compared to something like pea gravel gives it more void space between individual stones, which is why it's noticeably lighter per cubic yard than a densely packed crushed material.
This instrument follows the same volume-to-weight pattern used across this site's aggregate calculators: length times width times depth converts to cubic yards, then multiplies by density to get tons. The built-in density default of 1.35 tons per cubic yard is a typical figure for decorative river rock, but the real number varies with rock size — larger stones pack with more air gaps between them than smaller ones — so adjust the Material density field to match your supplier's actual product if you know it.
Coverage depth is a matter of the look you're going for as much as engineering: a thin 2 to 3 inch decorative topping over a garden bed uses noticeably less material than a thicker 4 to 6 inch functional layer meant to suppress weeds or line a dry creek bed that occasionally carries real runoff. Landscape fabric laid beneath the rock is common practice to slow weed growth and keep the stone from working its way into the soil beneath it over time.
- Enter Area length (ft) and Area width (ft) — the garden bed, border, or dry creek footprint to be covered.
- Enter Depth (in) — thinner for a decorative topping, deeper for a functional weed-suppressing or drainage layer.
- Adjust Material density (tons/yd³) if your supplier specifies a different figure than the 1.35 default; larger stone tends to run lighter, smaller stone denser.
- Read Volume (cubic yards) and River rock needed (tons) beneath the inputs.
Worked example — a 15 × 6 ft dry creek bed accent
Enter 15 into Area length (ft), 6 into Area width (ft), and 3 into Depth (in) — a shallow decorative dry-creek-bed accent area. Volume works out to 15 × 6 × 0.25 = 22.5 ft³, which is 0.8333 cubic yards after dividing by 27.
At the default density of 1.35 tons per cubic yard, River rock needed (tons) reads 1.125 — a modest order for an accent-scale feature. A larger functional dry creek bed or a thicker decorative layer would scale the same formula up proportionally with area and depth.
Questions
How thick should a river rock layer be?
A thin 2 to 3 inch layer is typical for a purely decorative topping over a garden bed, while a functional dry creek bed or a layer meant to meaningfully suppress weeds is usually built up thicker, often 4 to 6 inches, so soil and weeds don't show through as the rock settles over time. There's no single correct depth — it depends on the look and function you're after for that specific area.
What's the difference between river rock and pea gravel?
River rock is generally larger and more variably sized — often ranging from about 1 inch up to several inches across — while pea gravel is small, uniformly sized rounded stone roughly the size of garden peas. Both are naturally rounded and water-worn rather than crushed, but river rock's larger scale reads as a bolder, chunkier landscaping feature, while pea gravel is more often used as a finer groundcover or bedding material.
Why does river rock density vary with stone size?
Larger stones leave bigger gaps between individual pieces when poured or spread, so a cubic yard of large river rock actually contains more empty void space, and therefore less solid stone by weight, than the same volume of smaller stones packed more tightly together. That's why this calculator's density default is disclosed as typical rather than fixed — adjust it toward the lower end of the range for larger rock, higher for smaller.
Should I buy river rock bagged or in bulk by the ton?
For a small accent area, bagged river rock from a garden center is often more convenient despite costing more per ton, while a larger area — anything beyond roughly a cubic yard or two — is typically far more cost-effective ordered in bulk by the ton from a landscape supplier, which is exactly the figure this calculator returns.
Do I need landscape fabric underneath river rock?
It's common, standard practice for a decorative or weed-suppressing installation — a fabric barrier beneath the rock slows weed growth from below and keeps the stone from gradually sinking into the underlying soil over time. It isn't strictly required for a purely functional dry creek bed meant to carry occasional water flow, where fabric can sometimes be dislodged by that same flow.