Area and depth to cubic yards and tonnage, for gravel, crushed stone, sand, river rock or topsoil.
Aggregate is sold by volume in some places and by weight in others, which is why the conversion matters. Volume is straightforward — area × depth, with 27 cubic feet to the cubic yard. Weight depends on the material's bulk density, and that is where the estimate gets softer.
A 20 × 10 ft area at 4 inches deep is 66.7 cubic feet, or 2.47 cubic yards. At a typical gravel density of about 105 lb per cubic foot, that is around 3.5 US tons.
| Material | lb/ft³ | Approx. tons per cubic yard |
|---|---|---|
| Pea gravel | ~105 | 1.4 |
| Crushed stone / road base | ~100 | 1.35 |
| Crushed limestone | ~105 | 1.4 |
| River rock | ~100 | 1.35 |
| Sand | ~100 | 1.35 |
| Topsoil | ~80 | 1.1 |
Treat these as approximate. Bulk density varies with stone size, how angular the pieces are, how much fine material fills the voids, and — significantly — moisture content. Wet aggregate can weigh 10 to 15% more than the same volume dry, which is a real difference on a lorry load. Where you can, order by the cubic yard rather than by weight.
| Application | Depth |
|---|---|
| Decorative bed topping | 2 in (50 mm) |
| Garden path, foot traffic | 2–3 in (50–75 mm) |
| Driveway top layer | 3–4 in (75–100 mm) |
| New driveway, total build-up | 8–12 in (200–300 mm) in layers |
| Paver or slab base | 4–6 in (100–150 mm) compacted |
A gravel driveway that lasts is not one deep layer of the same material. It is typically three: a base of large crushed stone, often 3 to 4 inches of clean 2-inch material, for drainage and load spreading; a middle layer of smaller stone; and a top layer of a well-graded crushed stone that compacts into a firm surface. Each layer is compacted before the next goes down.
Rounded stone — pea gravel and river rock — never locks together. It stays loose, migrates under tyres and gets pushed to the edges. It is fine for decoration and drainage and poor for anything driven on. Angular crushed stone with a range of sizes, including fines, is what compacts into a stable surface, because the angular faces interlock and the fines fill the voids.
Whatever goes on top, the subgrade decides how long it lasts. Remove topsoil and organic matter, which will decompose and settle. Compact the subgrade. On soft or clay ground, a geotextile fabric between soil and stone is worth the modest cost — it stops the stone being pumped down into the mud over time, which is the usual way a gravel driveway disappears.
Slope the surface slightly for drainage, about a quarter inch per foot away from any structure. Standing water is what destroys gravel surfaces, freeze-thaw or not.
Add about 10% for compaction and settlement — loose delivered material occupies more volume than it will once rolled. Suppliers often price by the ton with a minimum delivery, so it is worth calculating both figures and asking which is cheaper for your quantity. And check access: a full lorry needs room to tip, and where it can put the pile determines how far you will be barrowing.
About 1.4 tons for most gravels and crushed stone, and roughly 1.1 for topsoil, which is lighter. The figure comes from bulk density — around 105 lb per cubic foot for gravel, times 27 cubic feet per yard, divided by 2,000 lb per ton. Treat it as approximate: stone size, angularity, fines content and especially moisture all shift it, and wet aggregate can weigh 10 to 15% more than dry.
The top layer is typically 3 to 4 inches, but a driveway built to last is 8 to 12 inches of total build-up in compacted layers — large crushed stone at the base for drainage and load spreading, progressively smaller above, and a well-graded crushed top layer. Each layer should be compacted before the next goes on. A single deep layer of one material does not perform the same way.
Angular crushed stone with a range of sizes including fines. The angular faces interlock and the fines fill the voids, so it compacts into a firm surface. Avoid pea gravel and river rock for anything driven on — rounded stone cannot lock together, so it stays loose, migrates under tyres and ends up pushed to the edges. Rounded stone is good for decoration and drainage and poor for traffic.
On soft or clay ground it is worth the modest cost. A geotextile separates the stone from the soil beneath and stops the stone being pumped down into the mud under repeated loading, which is the usual way a gravel driveway gradually disappears. On firm, well-draining ground it matters much less. Either way, strip the topsoil and organic matter first and compact the subgrade — that matters more than the fabric.
By volume where the supplier allows it, because bulk density varies with moisture and a rained-on load weighs more without containing more material. If they only sell by the ton, calculate both figures and check the conversion they are using. Add about 10% either way for compaction and settlement, since loose delivered material takes up more space than it will once rolled.
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