River Rock Calculator
Cubic yards & tons of decorative river rock
Adding decorative river rock to beds, borders or a dry creek? Enter the area and depth to get the cubic yards, tons and bags to order. Below: how stone size changes the depth you need, a coverage chart, what it costs against mulch over ten years, and where rock is the wrong choice.
How deep should river rock be?
Depth follows stone size, not preference. You need roughly two layers of stone to hide what is underneath, so bigger stones need a deeper bed.
| Stone size | Depth | Typical use |
|---|---|---|
| ⅜ to ¾ in | 2 in | Paths, tight borders |
| 1 to 2 in | 2 to 3 in | Decorative beds, the common choice |
| 2 to 4 in | 3 to 4 in | Dry creek beds, splash zones |
| 4 to 8 in | 4 to 6 in | Feature areas, erosion control |
Going shallower than this to save money is a false economy: the fabric or soil shows through between stones, and the bed looks patchy from the day it is laid.
River rock coverage chart
| Depth | Cubic yards | Tons | 0.5 ft³ bags |
|---|---|---|---|
| 2 in | 0.68 yd³ | 0.92 | 37 |
| 3 in | 1.02 yd³ | 1.38 | 55 |
| 4 in | 1.36 yd³ | 1.83 | 74 |
Turned around, one ton of river rock covers about 108 ft² at 2 inches or 72 ft² at 3 inches. Larger stones cover a little less than these figures because they nest with bigger voids between them.
Worked example: a 15 × 8 ft foundation bed
A bed along the front of a house, 15 ft long and 8 ft deep, is 120 ft² at a 3-inch depth with 1 to 2 inch stone:
| Item | Working | Order |
|---|---|---|
| Volume plus 10% | 120 × 0.25 ft × 1.1 | 1.22 yd³ |
| As weight | 1.22 × 1.35 | 1.65 tons |
| If bagged instead | 33 ft³ ÷ 0.5 | 66 bags |
| Landscape fabric | 120 ft² plus overlap | about 140 ft² |
| Edging | perimeter, three sides | about 31 ft |
66 bags at $5 to $9 each is $330 to $594, against roughly $90 to $180 for the same stone in bulk plus delivery. Bags win only for a container or a repair.
River rock vs mulch
Every decorative rock calculator eventually runs into this comparison, and it deserves a straight answer.
This is the real decision, and the honest answer is that rock is not the low-maintenance option people assume.
| River rock | Mulch | |
|---|---|---|
| Upfront cost per 100 ft² | $75 to $200 | $25 to $60 |
| Replacement | Permanent | Top up yearly |
| 10-year cost | Roughly the same | Roughly the same |
| Soil health | Adds nothing | Feeds soil as it breaks down |
| Temperature | Reflects heat, warms soil | Insulates, keeps soil cool |
| Weeds | Seed in the voids, hard to pull | Easy to pull, smothered by refresh |
| Debris | Leaves lodge between stones | Leaves compost in place |
| Removing it later | Very hard work | Easy |
Rock costs more upfront and is not replaced, so over about ten years the two roughly even out. Where rock genuinely wins is around downspouts, in dry creek beds, on slopes that wash out, and anywhere near a firebreak. Where it loses is in planted beds: it reflects heat onto foliage, adds nothing to the soil, and once weeds seed into the gaps they are far harder to pull than from mulch.
The decision to think hardest about is that rock is close to permanent. Removing a rock bed years later is genuinely miserable work, whereas mulch simply breaks down.
Fabric, edging and dry creek beds
- Always lay fabric underneath. Without it the stones sink into the soil and you lose visible depth every year.
- Fabric is not a weed guarantee. It stops weeds from below; the ones that matter blow in on top and root in the debris that collects between stones. Plan on blowing leaves out each autumn.
- Use a hard edge so rock does not migrate into the lawn, where it will find your mower blade.
- For a dry creek bed, vary the stone size — larger 4 to 8 inch stones along the edges and 1 to 3 inch through the middle reads as natural, while one uniform size reads as a trench full of gravel.
- Excavate rather than mound, so the finished surface sits flush with the surrounding grade.
River rock or pea gravel?
Both are rounded and smooth, and the difference is size and purpose. Pea gravel is small, comfortable underfoot and suited to paths and patios where people walk. River rock is larger, more decorative and better where water moves: splash zones, dry creeks and drainage channels. River rock is not pleasant to walk on and works loose underfoot, so it is a poor surface choice.
How this river rock calculator works out its numbers
Volume is area × depth at 27 ft³ per cubic yard, with 10% added by default for uneven spread. Bag counts assume a 0.5 ft³ bag.
- Density is 100 lb/ft³, giving 1.35 tons per cubic yard, the same constant as the pea gravel calculator. Real river rock runs 90 to 110 lb/ft³ and larger grades sit at the lower end because they nest with bigger voids.
- Depth guidance is driven by stone size, since roughly two layers of stone are needed to hide the fabric beneath. Larger stone therefore needs a deeper and more expensive bed.
- Coverage per ton is geometric and will run slightly optimistic for stone above about 2 inches.
- The rock versus mulch comparison uses US planning prices from September 2026 and a ten-year horizon with annual mulch top-ups. Local prices vary widely, particularly for decorative and imported stone.
Reviewed September 2026.
Figures reviewed . Every worked example on this page is checked against the calculator above.
River Rock Calculator: frequently asked questions
How much does a ton of river rock cover?
About 108 ft² at 2 inches deep or 72 ft² at 3 inches. Larger stones cover a little less because they nest with bigger voids between them.
How deep should river rock be?
2 inches for small ⅜ to ¾ inch stone, 2 to 3 inches for the common 1 to 2 inch grade, and 3 to 4 inches for 2 to 4 inch stone. You need roughly two layers of stone to hide the fabric underneath.
How much river rock do I need for a bed?
A 15 × 8 ft bed at 3 inches deep takes about 1.22 cubic yards or 1.65 tons including 10% for uneven spread. In bags that would be 66, which is well past the point where bulk is cheaper.
Is river rock better than mulch?
It depends on the job. Rock wins around downspouts, in dry creek beds and on slopes that wash out. Mulch wins in planted beds because it feeds the soil, keeps it cool and is far easier to weed. Over ten years the costs are similar.
Is river rock good for drainage?
Yes. The rounded shape leaves large voids that let water move freely, which is why it suits dry creek beds and downspout splash areas. For a buried French drain, washed #57 crushed stone is the more common choice.
Do I need fabric under river rock?
Yes. Without it the stones work down into the soil and the bed loses visible depth each year. Be aware fabric only stops weeds from below; airborne seeds still root in the debris that collects between stones.
River rock or pea gravel, which should I use?
Pea gravel for anywhere people walk, since it is small and comfortable underfoot. River rock for decorative beds, dry creeks and splash zones, where its larger size handles moving water and looks more deliberate.
Can you put river rock over grass?
Not directly. Kill or strip the grass first, then lay fabric. Rock laid over living turf sinks unevenly as the grass dies and decomposes, and you get a lumpy bed within a season.