How the number is worked out
Area times depth gives cubic feet, divided by 27 gives cubic yards, multiplied by the density gives tons. Rounded stone packs a little looser than crushed, so most river rock lands near 1.4 tons a cubic yard; large cobbles sit closer to 1.3. Each bed is measured on its own and added up, then the waste allowance goes on the total.
area (ft²) × depth (ft) ÷ 27 × density (tons/yd³) = tons
Depth follows the stone
A decorative layer has one job: hide the ground and stay put. Pea-sized ⅜ inch pebbles do that at 2 inches. Three-quarter to one inch stone wants 2 to 3. One to three inch stone, the common landscape grade, needs 3. Anything sold as 3 to 5 inch is a cobble and needs 4 or more, and the coverage decreases as depth increases. These are starting estimates; confirm coverage for your supplier's actual stone size. Set the depth first; the price follows.
What it is not for
Never use river rock as a base under a driveway, a patio or a shed. Round stone rolls; a car pushes it out of the way and a compactor just makes it shift. Crushed stone is angular and locks. River rock is for beds, borders, dry creek beds, splash zones under downspouts and around a foundation where you want drainage without a mud line.
Fabric underneath
Lay landscape fabric before the stone. Without it the rock works down into the soil within a few seasons, weeds come up between the stones, and you end up buying another ton to top it up. Where the bed drains a downspout, use a permeable fabric, not plastic sheet.
Depth and coverage by stone size
| Stone | Depth | One ton covers |
|---|
| ⅜ in pea pebbles | 2 in | about 115 ft² |
| ¾ to 1 in | 2 to 3 in | 75 to 115 ft² |
| 1 to 3 in landscape rock | 3 in | about 75 ft² |
| 3 to 5 in cobbles | 4 in or more | about 60 ft² |
Questions
How much does a cubic yard of river rock weigh?
The default estimate is 2,800 pounds per cubic yard; ask the supplier for the actual bulk weight. Check your truck's payload label and subtract occupants and other cargo before loading.
How deep should river rock be?
Start with the size-specific estimates in the table, then confirm depth and coverage with the supplier. Larger cobbles may need a deeper layer to hide the ground; there is no single depth multiplier that fits every grading.
Can I use river rock for a driveway or a paver base?
No. It is round, so it does not lock together and will not compact. Use crushed stone for anything that gets driven on or built on.
Tons or cubic yards — which do I order?
Whichever the yard quotes; the ticket shows both. Decorative stone is nearly always priced by the ton, and bagged stone by the half-cubic-foot bag.
Other calculators
The same ticket, the same assumptions on screen, for whatever else the job needs.
Concrete slabs, footings, columns and stepsGravel driveways, bases and drainage stoneMulch beds and trees, by the yard or the bagAsphalt hot mix by the tonTopsoil beds, lawns and levellingFill dirt holes, grades and backfill, with settlingCompost lawn top-dressing and bed amendingSand paver bedding, play sand and fillCubic yards any volume, in every unitRebar bars, sticks, laps and weight