Whether it is a load of crushed rock for a base, decorative stone for a garden or larger rock for erosion control, you need to know both the volume and the weight before calling the quarry. Different rocks have very different densities: basalt is about 20% heavier than limestone and lava rock is roughly half the weight of either.
How to use the 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 |
|---|---|---|---|
| Crushed stone | 1,602 | 100.0 | 1.35 |
| Granite, crushed | 1,650 | 103.0 | 1.39 |
| Basalt, crushed | 1,954 | 122.0 | 1.65 |
| Limestone, crushed | 1,554 | 97.0 | 1.31 |
| Sandstone, broken | 1,510 | 94.3 | 1.27 |
| River rock | 1,600 | 99.9 | 1.35 |
| Pea gravel | 1,520 | 94.9 | 1.28 |
| Lava rock | 800 | 49.9 | 0.67 |
| Marble chips | 1,570 | 98.0 | 1.32 |
| Rip rap / large rock | 1,700 | 106.1 | 1.43 |
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: Crushed stone, Granite, crushed, Basalt, crushed, Limestone, crushed … |
| 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: Crushed stone; Custom density: 1,600 kg/m³; Area shape: Rectangle / square; Length (or diameter): 20 ft; Width: 10 ft; Depth: 4 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 = 200 ft²; Volume needed = 2.716 yd³; Weight needed = 3.667 US ton; Estimated cost = $165.02.
Frequently asked questions
How do I calculate how much rock I need?
Multiply length × width × depth to get the volume, add 5–10%, then multiply by the rock's bulk density for the weight.
How many tons of rock are in a cubic yard?
Usually 1.2–1.5 US tons for crushed rock and about 0.7 tons for lava rock.
What depth for a rock garden?
2–3 in for decorative stone over landscape fabric.
What formula does the Rock Calculator use?
Volume = area × depth × (1 + waste).