River Rock Calculator for Landscaping Beds
Updated 2026-08-01 · Yardly
Estimate river rock the same way as any spread material: square feet × depth in inches ÷ 324 = cubic yards, then multiply by about 1.2–1.4 to get tons. A 10 × 12 ft bed at 3 inches works out to 1.1 yards, or roughly 1.5 tons. The part most estimates get wrong isn’t the arithmetic — it’s picking a depth without accounting for stone size.
The formula, and the tons conversion
Square feet × depth (inches) ÷ 324 = cubic yards Cubic yards × 1.2 to 1.4 = tons
The 324 comes from unit math: one cubic yard is 27 cubic feet, which spread 1 inch deep covers 324 square feet. The tons factor exists because most stone yards sell by weight while you measure by area.
Why the tons range is wide: rounded river rock doesn’t pack. Crushed angular stone interlocks and gets close to 1.5 tons per yard; smooth stones roll into loose arrangements with large voids between them, and the bigger the stone, the bigger the voids. Fine pea-size gravel sits near the top of the range, 3–5 inch cobbles near the bottom. If your supplier quotes a density for the specific product, use theirs — it beats any generic factor. The river rock calculator runs both conversions, and the gravel calculator covers angular crushed stone if you’re comparing.
Coverage per ton, worked from those numbers:
| Depth | Sq ft per ton |
|---|---|
| 2 in | 115–125 |
| 3 in | 75–85 |
| 4 in | 55–65 |
Depth is set by stone size, not by taste
A rock layer has to be thicker than the rocks in it, or you get a single course of stones with soil grinning through the gaps. A workable rule of thumb: plan on at least twice the diameter of your largest stone.
| Stone size | Practical minimum depth | Typical use |
|---|---|---|
| ½–1 in | 2 in | Tight decorative cover, between pavers |
| 1–2 in | 3 in | Beds, borders, general ground cover |
| 2–3 in | 3–4 in | Dry creek beds, drip lines, drainage |
| 3–5 in | 5–6 in | Accent areas, swale bottoms, erosion points |
This is where budgets get away from people. Going from 1-inch stone at 3 inches deep to 3-inch cobbles at 6 inches deep doubles the volume for the same square footage — and cobbles cost more per ton. Choosing a large stone is a materials decision, not just a look.
River rock is not mulch, and the research is fairly clear
There’s a persistent idea that rock is “permanent mulch” — spread it once, never mulch again. The evidence doesn’t really support it for planted beds.
Work summarized in Colorado State University’s Mulching GardenNotes draws the line at stone size: gravel under about half an inch in diameter has been shown to suppress weeds and reduce evaporation about as well as wood chips, and even a thin layer of it can substantially increase how much rainfall soaks in. Larger stones don’t do this — they increase runoff instead, and the summary is direct that stones bigger than roughly half an inch “do not confer the benefits of mulch.” Nearly all product sold as landscaping river rock is 1–3 inches.
The practical downsides pile up over years rather than showing up on install day. K-State Extension’s rock mulch article catalogs them: rock absorbs and re-radiates heat, driving up soil temperature and water demand for nearby plants; wind-blown soil and seed silt into the gaps and create an ideal seedbed on top of the stone; rock on a slope migrates downhill and exposes the fabric underneath; and removing silted-in rock later is a stone-by-stone job or a loader job.
None of that makes river rock a bad material — it makes it a material for specific places:
- Good: dry creek beds and swales, drip lines under eaves, downspout splash zones, side yards and utility strips, borders around hardscape, water features
- Poor: beds of thirsty perennials, anywhere adjacent to lawn (mower + loose stone is a safety and blade problem), slopes without terracing, children’s play areas
- Better served by wood mulch: shrub and perennial beds where soil improvement and rejuvenation pruning matter — see mulch for garden beds for depths and the mulch calculator for volumes
Worked example: drip line plus a small dry creek
A house needs a stone strip under the eaves and a short dry creek carrying a downspout to the back fence.
| Feature | Area | Depth | Volume |
|---|---|---|---|
| Drip line, 2 ft × 40 ft, 1-in stone | 80 sq ft | 3 in | 0.74 yd³ |
| Dry creek, avg 4 ft × 18 ft, 2–3 in stone | 72 sq ft | 4 in | 0.89 yd³ |
Total 1.63 yd³ → add 10% for settling and irregular edges → 1.8 yd³, or about 2.3 tons. Round up to what the yard sells in: 2 yards or 2.5 tons.
Bags only make sense at tiny volumes. At the common 0.5 cubic foot bag size, one cubic yard is 54 bags — the crossover to bulk delivery happens somewhere around a third of a yard.
Before the rock goes down
- Kill and remove existing weeds, roots included. Anything left will come through, fabric or not.
- Set an edge. Steel, aluminum, or a mowing strip keeps stone out of the turf. This is the single biggest determinant of whether the installation still looks intentional in three years.
- Check the slope. On anything steeper than gentle, use larger stone or terrace it — small stone walks downhill.
- Grade the creek bed first. A dry creek only works if it actually falls toward its outlet; stone doesn’t create drainage, it just protects a channel that already drains. For base-layer work under hardscape rather than decorative cover, gravel for a patio base covers compaction and depth.
Keep reading
- Mulch for garden beds — depths, coverage, and why organic mulch still wins around plants.
- Gravel for a patio base — the structural cousin of this job, with compaction requirements.
- The landscape material calculators guide maps each Yardly tool to the material it estimates.
Frequently asked questions
How deep should river rock be for landscaping?
2 inches for a purely decorative layer over a firm, weed-free surface; 3 inches where you want the ground fully hidden and some weed suppression; 4–6 inches for dry creek beds and drainage runs where water moves through the stone. Larger stone needs the deeper end of each range — a 3-inch layer of 3-inch cobbles is a single sparse course. The [river rock calculator](/calculators/river-rock) converts area and depth to yards and tons.
How many square feet does a ton of river rock cover?
Roughly 115–125 sq ft at 2 inches, 75–85 sq ft at 3 inches, and 55–65 sq ft at 4 inches. The math: a ton is about 0.7–0.8 cubic yards of rounded stone, and one cubic yard spread 1 inch deep covers 324 sq ft. Ranges are wide because rounded stone packs loosely and larger sizes leave bigger voids.
Does river rock stop weeds?
It suppresses them at first and gets worse over time. Wind-blown soil and seed collect in the gaps between stones and create a seedbed sitting on top of your rock — and weeds rooted through stone and fabric are far harder to pull than weeds in mulch. The [K-State Extension write-up on rock mulch](https://www.johnson.k-state.edu/lawn-garden/agent-articles/miscellaneous/rock%20mulch%20a%20solution%20or%20a%20problem.html) is blunt about the maintenance curve.
Is river rock a good mulch for planting beds?
Usually not. Research summarized in [Colorado State University's Mulching GardenNotes](https://cmg.extension.colostate.edu/Gardennotes/245.pdf) found gravel only performs like mulch — suppressing weeds and cutting evaporation comparably to wood chips — when stones are under about half an inch across. Larger stone doesn't confer those benefits, and bigger rock increases runoff rather than infiltration. Most river rock sold for landscaping is 1–3 inches, which puts it firmly in the decorative-and-drainage category.
Should I put landscape fabric under river rock?
It helps keep stone from sinking into soft soil, which is a real problem on bare ground. But it doesn't solve weeds long-term — seeds germinate in the silt above it — and aging fabric frays, shows through on slopes, and makes future planting or rock removal miserable. Use it under non-planted areas and drainage features; skip plastic sheeting entirely, which suffocates soil.