Decorative landscape rock replaces mulch in beds, xeriscapes and dry creek beds. It does not decompose, but it is heavy, so a bed that needs two cubic yards of mulch might need well over two tons of stone. Rock sizes from ½-inch pebbles to 3-inch cobbles are usually laid 2–3 inches deep, or about twice the diameter of the stones so that the fabric underneath is hidden.
How to use the Landscape 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 | 1,600 | 99.9 | 1.35 |
| Pea gravel | 1,520 | 94.9 | 1.28 |
| Crushed granite | 1,650 | 103.0 | 1.39 |
| Decomposed granite | 1,600 | 99.9 | 1.35 |
| Lava rock | 800 | 49.9 | 0.67 |
| Marble chips | 1,570 | 98.0 | 1.32 |
| Mexican beach pebbles | 1,600 | 99.9 | 1.35 |
| Slate chips | 1,450 | 90.5 | 1.22 |
| Crushed limestone | 1,554 | 97.0 | 1.31 |
| Quartz chips | 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, Pea gravel, Crushed granite, Decomposed granite … |
| 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; Custom density: 1,600 kg/m³; Area shape: Rectangle / square; Length (or diameter): 15 ft; Width: 6 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 = 90 ft²; Volume needed = 0.917 yd³; Weight needed = 1.236 US ton; Estimated cost = $55.62.
Frequently asked questions
How deep should landscape rock be?
About 2 in for pebbles up to 1 in, 3 in for 1–2 in rock and 4 in or more for larger cobbles.
How much does a bag of landscape rock cover?
A 0.5 ft³ bag covers about 3 ft² at 2 in deep, so bulk delivery is usually cheaper for anything over a few square yards.
Is lava rock lighter?
Yes. Lava rock is porous and weighs about half as much as river rock for the same volume, so one ton covers roughly twice the area.
Should I use landscape fabric?
A woven fabric under the rock slows weeds and stops the stones sinking into the soil.
What formula does the Landscape Rock Calculator use?
Volume = area × depth × (1 + waste).