Gravel is ordered by volume or by weight, and both start the same way: area × depth gives the volume, then multiply by the material’s density for the tonnage. Add a little for settling and you have the delivery quantity. The only figure that varies by material is the density.
Step 1: the volume
Multiply the area by the layer depth — keep the depth in the same units. A 20 × 10 ft area is 200 sq ft; at 2 in (0.167 ft) deep that is 200 × 0.167 = about 33 cu ft, or 33 ÷ 27 = 1.2 cubic yards (0.95 m³).
Step 2: convert to tons
Most crushed stone and river pebble runs about 1.3–1.4 US tons per cubic yard(1.5–1.7 t/m³). So the 1.2 yd³ above is roughly 1.2 × 1.4 = 1.7 US tons (1.5 t). Add a 10% settling allowance and you order about 1.9 US tons (1.7 t).
| Material | US tons / yd³ | t / m³ |
|---|---|---|
| Crushed stone / pea gravel | 1.3–1.4 | 1.5–1.7 |
| Decomposed granite | ~1.2 | ~1.4 |
| Bark mulch | ~0.25 | ~0.3 |
Gravel Calculator
Enter the area, depth and material — it returns the cubic yards (m³), US tons (tonnes) and bags, with a settling allowance built in.
How deep should the layer be?
About 1.5–2 in (40–50 mm) for decorative ground cover and paths — deep enough to hide the soil, shallow enough to walk on — and 3–4 in (75–100 mm) for driveways, ideally in two compacted layers over a proper sub-base. Too shallow shows bald patches; too deep is hard to walk on and wastes stone.
Put something underneath
A weed barrier (geotextile) under decorative gravel keeps soil and stone apart and stops the gravel sinking into the ground within a season — it usually saves a full re-top within a few years. Driveways need a compacted sub-base; the gravel is the wearing surface, not the structure.
Bags or bulk delivery?
Above roughly half a cubic yard, bulk (loose or bulk-bag) delivery is far cheaper per ton than small bags. A standard bulk bag holds about 1 cubic yard (0.7–0.9 m³) depending on the stone. Small 50 lb (40 kg) bags suit top-ups and spots a truck can’t reach.