Gravel calculator

Gravel is ordered by weight. You measure a volume, the supplier sells you tons, and the conversion between the two depends on the material: open washed stone weighs less per yard than crusher run packed with fines, and wet sand weighs more than dry. This calculator works out the volume from the area and depth, adds an allowance for compaction, then converts to tons using published densities.

How it is calculated

1. Area: length × width, or π × (diameter ÷ 2)² for a circle.
2. Volume = area × depth, with the depth converted from inches to feet (÷ 12) or centimetres to metres (÷ 100).
3. Add the compaction allowance, because loose material settles when it is rolled.
4. Weight = volume in cubic feet × the density of the material, ÷ 2,000 for US tons. The densities come from the EPA volume-to-weight conversion table: 100 lb/ft³ for dry gravel and crushed stone, 85–90 for crushed limestone, 95–100 for crushed granite, 90–110 for sand.
5. Cubic yards = cubic feet ÷ 27, so a ton of typical gravel is about three quarters of a yard.

Example

A 40 × 12 ft driveway at 4 inches of #57 crushed stone, with 10% for compaction: 480 ft² × 0.333 ft = 160 ft³, × 1.10 = 176 ft³, which is 6.52 cubic yards. At 95 lb/ft³ that is 16,720 lb, so 8.36 US tons (7.58 tonnes). At $35 a ton, about $293 of stone before delivery.

Why the density matters

A solid piece of limestone weighs about 165 lb per cubic foot, but a pile of crushed limestone weighs only 85–90, because a third to a half of the pile is air between the stones. How much air depends on the grading. Single-sized washed stone such as #57 stays open and drains, so it is light per yard and does not lock together. Crusher run contains everything from 3/4 inch down to dust, the fines fill the gaps, and it compacts into a hard surface at roughly 115 lb per cubic foot. Ask your supplier what conversion they use before you order: they weigh the truck, and their ticket, not this estimate, is what you pay for.

Layers for a driveway

A gravel driveway is built in layers, not one thick dump. The usual build is 4 inches of coarse base stone, then 3–4 inches of crusher run or dense-graded aggregate, then an inch or two of decorative topping if you want one. Each layer is spread thin and rolled: highway specifications call for at least 95% relative compaction, tested against a standard laboratory density, and the same principle applies to a driveway even if you never measure it. On clay or anywhere that stays wet, a geotextile between soil and stone stops the two mixing and roughly doubles the life of the surface.

Tons, yards and the delivery truck

For the same area poured rather than covered, the concrete calculator gives bags and cubic yards. A standard tandem dump truck carries 12–15 tons, roughly 9–11 cubic yards, and most suppliers charge a flat delivery fee regardless of load, so it is cheaper per ton to order in full loads. Gravel is heavy: a single cubic yard of crushed stone is about 1.3 tons, which is at the limit of a half-ton pickup. Two yards need a trailer or a delivery.

Frequently asked questions

Sources

1. US EPA: Standard volume-to-weight conversion factors — densities for gravel, crushed stone, limestone, granite and sand
2. INDOT: Certified Aggregate Technician Manual — particle density of limestone and the voids between aggregate particles
3. Caltrans standard specifications, section 26 Aggregate bases (95% relative compaction) — relative compaction and layer thickness for aggregate base