What the gravel and sand calculator does
Enter the length, width and depth of the area to fill and pick the material — gravel, sand or topsoil — and the calculator returns the volume in cubic metres and the weight in tonnes, which is how suppliers sell and deliver it. It takes the guesswork out of ordering for a driveway, a path, a patio sub-base, a raised bed, a sandpit or a drainage trench, and runs in your browser.
The calculation
Volume (m³) = length (m) × width (m) × depth (m)
Weight (t) = volume × bulk density
Bulk densities used:
Gravel 1.4 t/m³ Sand 1.6 t/m³ Topsoil 1.1 t/m³
Path 12 m × 1.2 m, 75 mm (0.075 m) deep, gravel:
volume = 12 × 1.2 × 0.075 = 1.08 m³
weight = 1.08 × 1.4 = 1.51 t → order 1.6–1.7 t with 10% allowanceDepth is the number most often entered wrongly — it is usually in millimetres or centimetres while the other dimensions are in metres. 75 mm is 0.075 m.
How deep?
| Use | Material | Typical depth |
|---|---|---|
| Decorative gravel over membrane | 10–20 mm gravel | 40–50 mm |
| Gravel path or drive surface | 10–20 mm gravel | 50–75 mm over a compacted base |
| Driveway sub-base (MOT type 1) | Crushed stone | 100–150 mm compacted |
| Patio / paving bedding | Sharp sand | 30–50 mm |
| Block paving laying course | Sharp sand | 30–40 mm |
| Sandpit | Play sand | 200–300 mm |
| French drain | 20–40 mm gravel | Trench depth minus pipe, typically 300+ mm |
| Raised bed / new lawn | Topsoil | 150–300 mm |
Density varies — order with a margin
- Densities depend on the stone type, grain size and moisture: wet sand is heavier than dry, crushed limestone differs from river gravel. The values used are typical for dry bulk material; check the supplier's figure if they give one.
- Compaction reduces volume. Sub-base and sand that will be compacted need about 20–25% more loose material than the finished depth suggests.
- Add 5–10% for spillage, uneven ground and settlement.
- Bulk bags are nominally 850 kg–1 tonne; loose loads are sold by the tonne or the cubic metre. Convert with the density to compare prices.
Irregular and circular areas
- Split an L-shaped or irregular area into rectangles, calculate each, and add the volumes.
- For a circle, the area is π × radius²; multiply by depth for the volume. The Circle Calculator gives the area directly.
- For a sloping trench, use the average depth.
Frequently asked questions
How many bulk bags do I need?
Divide the tonnes by the bag weight your supplier quotes (usually 0.85–1 t) and round up. Two bulk bags of gravel cover about 1.5 m³ — roughly 20 m² at 75 mm.
How much does a cubic metre of gravel weigh?
About 1.4 tonnes for typical 20 mm gravel; crushed stone sub-base 1.5–1.6 t; sand 1.5–1.7 t depending on moisture.
Should I lay a membrane under gravel?
For decorative areas and paths, yes — it stops gravel sinking into the soil and suppresses weeds. Under a compacted sub-base a geotextile separates layers and is standard on driveways.
Can I use the calculator for concrete or mulch?
Volume, yes. For weight, concrete is about 2.4 t/m³ and bark mulch around 0.3–0.5 t/m³; the Concrete Calculator handles concrete including bag counts.
Why does the delivered amount look smaller than I expected?
Material settles and compacts in transit and on laying; a loose tonne of gravel occupies less than 0.7 m³ once raked and walked on. The margin covers it.
Are my figures stored?
No. The calculation runs in your browser.