This calculator turns an area and depth into the amount of gravel (aggregate) you need to buy. Enter the length and width in metres or feet and the depth in millimetres, and it returns the volume in cubic metres plus estimates in tonnes and cubic yards — useful for paths, driveways, borders and sub-bases.
How it works
The tool converts your inputs to metres, multiplies them for a volume, then applies fixed density and unit factors:
volume (m³) = length (m) × width (m) × (depth_mm ÷ 1000)
tonnes = volume × 1.6 (typical loose-gravel bulk density)
cubic yards = volume × 1.30795
If you enter the area in feet, each dimension is first multiplied by 0.3048 to convert to metres. Depth is always taken in millimetres.
Example
For a path 10 m long, 2 m wide, at 50 mm depth:
- volume = 10 × 2 × 0.05 = 1.0 m³
- weight = 1.0 × 1.6 = 1.6 tonnes
- cubic yards = 1.0 × 1.30795 = 1.31 cubic yards
| Depth | Volume (10 × 2 m) | Tonnes |
|---|---|---|
| 40 mm | 0.8 m³ | 1.28 t |
| 50 mm | 1.0 m³ | 1.6 t |
| 75 mm | 1.5 m³ | 2.4 t |
The weight assumes a typical loose-gravel density of about 1.6 t/m³; actual density varies by stone and moisture, so order a small margin. Everything runs in your browser and nothing is uploaded.
Choosing the right gravel depth for your project
Depth is the biggest variable and it depends on what the gravel needs to do:
| Application | Recommended depth |
|---|---|
| Decorative path or border | 30–40 mm |
| Garden path (light foot traffic) | 40–50 mm |
| Driveway (regular car use) | 50–75 mm on compacted sub-base |
| Driveway sub-base (hardcore) | 100–150 mm compacted |
| Drainage French drain | 150–300 mm depending on pipe depth |
For driveways, a common approach is to lay 100–150 mm of hardcore (compacted crushed stone or MOT Type 1) as a sub-base, then 40–50 mm of decorative gravel on top. Enter each layer separately and add the results, or enter the total combined depth.
Stone type and density
Loose bulk density varies with stone type and whether the gravel is wet or dry:
- Pea gravel and rounded shingle — around 1.4–1.6 t/m³
- Crushed granite or limestone — around 1.6–1.7 t/m³
- MOT Type 1 (compacted crushed stone) — around 2.0–2.2 t/m³ once compacted
The calculator uses 1.6 t/m³, a reasonable midpoint for loose decorative aggregate. If your supplier quotes a different density for the specific stone, you can apply the same volume result manually: tonnage = volume × supplier density.
How much to order
Always order 5–10% more than the calculation suggests. Gravel settles into an uneven sub-surface, some spills during delivery and spreading, and coverage at boundaries is rarely perfectly efficient. Bags (usually 20–25 kg each) are convenient for small jobs; a bulk tonne bag or loose lorry delivery is more cost-effective above about 1 tonne. For a large driveway the lorry delivery price per tonne is typically significantly lower than bagged options.