Decorative stone estimator
River rock calculator
River rock is sold by the ton in most yards but spread by the square foot in most gardens, and the two only line up once you fix a depth. Pick your stone size, enter the area and the depth, and this converts between all of it: tons, cubic yards, cubic feet, cubic metres, bags and cost.
Bigger stone needs a deeper layer, so the size you choose changes the tonnage more than people expect. The size guide below the calculator gives the depth each grade actually wants.
Turning square feet into tons
Every river rock question is the same three-step conversion. Square feet × depth in feet gives cubic feet. Divide by 27 for cubic yards. Multiply by the density — around 1.35 tons per cubic yard for typical washed river rock — for tons.
A dry creek bed 30 ft long and 4 ft wide is 120 square feet. At 3 inches of 3/4-inch stone: 120 × 0.25 = 30 cubic feet, which is 30 ÷ 27 = 1.11 cubic yards, or 1.11 × 1.35 = 1.50 tons. Order a ton and a half and you are covered.
The same bed in 2-inch stone wants a deeper layer — say 4 inches. That is 120 × 0.333 = 40 cubic feet, or 1.48 cubic yards, and at 1.32 tons per yard, 1.96 tons. Same footprint, roughly 30% more stone, purely because the larger grade needs the extra depth.
The one number to remember. At about 1.35 tons per cubic yard, one ton of river rock is roughly 20 cubic feet — which covers 120 square feet at 2 inches deep, 80 square feet at 3 inches, or 60 square feet at 4 inches.
River rock coverage per ton
| Depth | 1 ton covers | 1 cubic yard covers | Tons per 100 sq ft |
|---|---|---|---|
| 1 in | 240 sq ft | 324 sq ft | 0.42 t |
| 2 in | 120 sq ft | 162 sq ft | 0.83 t |
| 3 in | 80 sq ft | 108 sq ft | 1.25 t |
| 4 in | 60 sq ft | 81 sq ft | 1.67 t |
| 6 in | 40 sq ft | 54 sq ft | 2.50 t |
| 8 in | 30 sq ft | 41 sq ft | 3.33 t |
Larger cobble beats these numbers slightly, because the voids between big rounded stones are bigger — expect maybe 5–10% more coverage per ton with 4–8 inch grades than the table suggests, and treat that as a bonus rather than something to design around.
Choosing a size
| Size | Typical use | Depth to order |
|---|---|---|
| 3/8"–3/4" | Paths, patio infill, planters, spots you walk on barefoot | 2 in |
| 1" | Beds and borders, ground cover around shrubs | 2–3 in |
| 1"–3" | The all-purpose decorative grade; dry creek beds, downspout splash zones | 3–4 in |
| 2" | Beds where you want visible individual stones and less scatter | 3–4 in |
| 2"–4" | Slopes, drainage swales, edges of water features | 4–6 in |
| 4"–8" | Cobble accents, erosion control, feature boulder fields | One stone deep |
Two practical notes. Stone under about an inch stays put underfoot but shows every weed seed, so lay fabric under it. Stone over about three inches is uncomfortable to walk on and awkward to rake, so keep it out of paths and use it where it is seen rather than crossed.
Common questions
How many tons of river rock do I need for 100 square feet?
At 2 inches deep, 0.83 tons; at 3 inches, 1.25 tons; at 4 inches, 1.67 tons — all at 1.35 tons per cubic yard. Since most suppliers set a minimum order, anything under a ton usually means paying for a ton anyway.
How deep should river rock be?
Two to three times the stone diameter, with 2 inches as the floor. Small 3/4-inch stone works at 2 inches; 1"–3" wants 3–4 inches; large cobble is laid a single stone deep. Shallower than that and the fabric or soil shows through as soon as the stone is disturbed.
How many cubic yards is a ton of river rock?
About 0.74 cubic yards, since a cubic yard weighs roughly 1.35 tons. Inverted: one cubic yard is about 1.35 tons, and 20 cubic feet is about one ton. Suppliers who quote by the yard and suppliers who quote by the ton are describing the same pile — the calculator shows both so you can compare quotes directly.
Is river rock heavier than crushed gravel?
Slightly lighter per cubic yard, typically. Rounded stones cannot interlock the way angular crushed stone does, so a yard of river rock contains more air — around 1.3–1.35 tons against roughly 1.4 for 3/4-inch crushed stone. The individual rocks are not lighter; the packing is looser. See the gravel calculator for the crushed grades.
Do I need landscape fabric under river rock?
For decorative beds, yes — it keeps the stone from sinking into soil and slows weeds. For drainage applications, use a permeable filter fabric rather than a solid weed barrier, or you will block the water you were trying to move. Fabric does not change the volume calculation, but skipping it means topping up sooner.