River rock is smooth, rounded stone tumbled by water, used for dry creek beds, drainage swales, borders and decorative ground cover. Because the stones are rounded they do not lock together like crushed gravel, so it is not suitable for driveways, but it is ideal anywhere water flows. Lay it about twice as deep as the average stone size so the ground does not show through.
How to use the River Rock Calculator
- Material
- Custom density
- Area shape
- Length (or diameter)
- Width
- Depth
- Extra for waste and compaction
- Priced by
- Price per weight
- Price per volume
- Every result field is editable: type into Volume needed or any other result and Depth plus every other field update to match.
Results update as you type, and every field accepts the units shown in its menu.
How it works
The calculator finds the area of your rectangle, circle or triangle, multiplies it by the depth and adds the waste allowance to get the volume. Multiplying by the density of the chosen material gives the weight, and the price you enter turns either one into a cost.
Densities used
| Material | kg/m³ | lb/ft³ | US tons per yd³ |
|---|---|---|---|
| River rock ¾–1½ in | 1,600 | 99.9 | 1.35 |
| River rock 1½–3 in | 1,570 | 98.0 | 1.32 |
| River rock 3–5 in (cobble) | 1,550 | 96.8 | 1.31 |
| Pea gravel (river) | 1,520 | 94.9 | 1.28 |
| Mexican beach pebbles | 1,600 | 99.9 | 1.35 |
Good to know
A U.S. (short) ton is 2,000 lb; a metric tonne is 1,000 kg (2,204.6 lb). Quarries in the U.S. sell by the short ton, so check which one your quote uses.
Tips for an accurate estimate
- Sketch the job and split irregular areas into rectangles, circles and triangles before you measure.
- Add a waste allowance – typically 5–10% for simple layouts and 15–20% for diagonal, curved or heavily cut work.
- Check the coverage or yield printed on the product, because sizes and densities vary between manufacturers.
- Buy all units of a finished material (tile, brick, siding) from the same batch so colours match, and keep a few spares for repairs.
- Confirm local prices – quarry, lumber and steel prices vary widely by region and season.
Common mistakes to avoid
- Ordering exactly the calculated amount with no allowance for breakage, offcuts and settlement.
- Forgetting to subtract doors, windows and other openings – or subtracting small ones that still need cutting around.
- Confusing US short tons (2,000 lb) with metric tonnes (1,000 kg) when comparing quotes.
Inputs explained
| Field | What to enter |
|---|---|
| Material | Choose one: River rock ¾–1½ in, River rock 1½–3 in, River rock 3–5 in (cobble), Pea gravel (river) … |
| Custom density | Units: kg/m³, lb/ft³, g/cm³, lb/yd³ |
| Area shape | Choose one: Rectangle / square, Circle (length = diameter), Triangle (length = base, width = height) |
| Length (or diameter) | Units: ft, m, in, yd, cm |
| Width | Units: ft, m, in, yd, cm |
| Depth | Units: in, cm, mm, ft, m |
| Extra for waste and compaction | In % |
| Priced by | Choose one: Weight (per ton / tonne), Volume (per yd³ / m³) |
| Price per weight | Units: /US ton, /t, /lb, /kg |
| Price per volume | Units: /yd³, /m³, /ft³ |
Formula
Volume = area × depth × (1 + waste)Weight = volume × densityCost = weight × price per ton (or volume × price per yd³)Worked example
Inputs — Material: River rock ¾–1½ in; Custom density: 1,600 kg/m³; Area shape: Rectangle / square; Length (or diameter): 20 ft; Width: 4 ft; Depth: 3 in; Extra for waste and compaction: 10 %; Priced by: Weight (per ton / tonne); Price per weight: $45 /US ton; Price per volume: $60 /yd³.
Results — Area = 80 ft²; Volume needed = 0.815 yd³; Weight needed = 1.099 US ton; Estimated cost = $49.44.
Frequently asked questions
How deep should river rock be?
Around 2 in for ¾–1½ in stones and 3–4 in for 1½–3 in stones.
How much area does a ton of river rock cover?
About 80–100 ft² at 2 in deep.
Can I drive on river rock?
Not easily – rounded stones roll under tyres. Use crushed angular stone for driveways.
What formula does the River Rock Calculator use?
Volume = area × depth × (1 + waste).