How to use the river rock calculator
- Measure the bed. For curved beds, approximate with rectangles or circles, or walk the outline with a measuring wheel and estimate the average width.
- Choose your rock size from the material list. Larger stones leave bigger gaps, so a cubic yard of cobble weighs a little less than a cubic yard of small river rock.
- Set the depth. A good rule is a layer about twice as deep as the average stone, so the fabric below is fully covered.
- Add waste. 10% covers uneven ground and stone that sinks into soft soil.
Choosing a river rock size
- 3/4–1 inch: fine-looking mulch replacement for beds and between stepping stones. Depth 2 inches.
- 1–3 inches: the most common landscape size for beds and along foundations. Depth 3–4 inches.
- 3–5 inch cobble: dry creek beds, swales and downspout splash areas where water flow would wash out small stones. Depth 4–6 inches, often with larger boulders placed on top.
The formula
Cubic feet = area (sq ft) × depth (in) ÷ 12
Cubic yards = cubic feet ÷ 27 · Tons = cubic feet × density ÷ 2,000
River rock densities vary with size and stone type. The defaults here (95–102 lb/ft³, about 1.3–1.4 tons per cubic yard) sit slightly below the 105 lb/ft³ that The Engineering ToolBox lists for dry gravel, because large, rounded stones pack with more air between them. Many landscape suppliers quote 1.2–1.5 tons per yard; if yours gives a figure, type it in as a custom density.
Worked example
A foundation border is 30 ft long and 3 ft wide. You plan to use 1–3 inch river rock at 3 inches deep, with 10% extra.
- Area: 30 × 3 = 90 sq ft
- Volume: 90 × 3 ÷ 12 = 22.5 cu ft; with 10% = 24.75 cu ft
- Cubic yards: 24.75 ÷ 27 = 0.92 yd³
- Weight at 100 lb/ft³: 2,475 lb = 1.24 tons
- Bagged: 24.75 ÷ 0.5 = 49.5 → 50 bags of 0.5 cu ft
Fifty bags is a lot of lifting. When a project passes about one cubic yard, a bulk load from a landscape supply yard is usually cheaper and much faster.
Dry creek bed tips
- Dig the channel 6–12 inches deep with gently sloped sides, line it with fabric, and use a mix of sizes: cobble along the bottom and sides, smaller rock to fill gaps.
- Measure the area of the fabric, not the top opening, because rock covers the sloped sides too. Widening your width input by about 25% approximates the extra side area.
- If the creek bed is also meant to carry water underground, consider a perforated pipe; see the French drain gravel calculator.
General tips
- Fabric first. River rock is hard to clean once soil and leaves work into it. A woven landscape fabric keeps it separate from the soil.
- Check color when wet. River rock looks much richer when wet. Ask to see a wet sample before ordering a full load.
- Mind the heat. Rock beds absorb and reflect heat, which can stress plants beside south-facing walls.
Frequently asked questions
How much area does a ton of river rock cover?
At about 1.35 tons per cubic yard, one ton is about 20 cubic feet. That covers roughly 80 sq ft at 3 inches deep or 60 sq ft at 4 inches deep.
How deep should river rock be?
About twice the size of the average stone: 2 inches for 3/4–1 inch rock, 3–4 inches for 1–3 inch rock, and 4–6 inches for 3–5 inch cobble.
How many bags of river rock make a yard?
A cubic yard is 27 cubic feet, so it takes 54 bags of 0.5 cu ft, or 36 bags of 0.75 cu ft.
Do I need landscape fabric under river rock?
It is strongly recommended. Fabric stops the rock from sinking into soil and slows weeds coming up from below, which keeps the bed clean for years.
Is river rock heavier than mulch?
Much heavier. A cubic yard of river rock weighs around 2,700 lb, while a cubic yard of wood mulch is typically a few hundred pounds, so plan for heavier loads and smaller wheelbarrow trips.