How many tons of gravel in a cubic yard?

How the number is worked out

Start with the volume you want in place: area × finished depth. A 20 ft × 20 ft driveway at 4 in is 400 × 0.333 = 133 cubic feet, or 4.94 cubic yards compacted.

Then two adjustments turn that into an order:

1. Compaction. Loose crushed stone carries 35–40% air voids. Run a plate compactor over it and that drops to 20–25%, which means the pile gets shorter. Dense-graded base has to be ordered about 25% over the finished volume — 4.94 becomes 6.2 cubic yards.
2. Weight. Yards sell gravel by the ton, so the cubic yards get multiplied by density. At 2,950 lb/cu yd for crusher run, 6.2 cubic yards is about 9.1 tons.

The compaction mistake

This is the error that actually costs people a return trip. Almost every gravel calculator takes your finished depth, converts it straight to volume, and stops. Order that figure and you will be short by a fifth — you get three-quarters of the driveway to the right depth and run out.

The related field mistake is placing it all at once. Compact in lifts of 4–6 inches of loose material, which settles to 3–4 inches. A 10 in base poured in one go leaves the bottom half loose no matter how long you run the plate over the top, and that is what makes a driveway develop ruts in year two.

Rounded stone is the exception. Pea gravel and river rock will not interlock, so they are never compacted and get no allowance at all. Applying a base compaction factor to pea gravel just over-orders.

Density is per stone, not universal

The other flattening you see everywhere is "gravel weighs about 1.4 tons per yard". Typical published supplier figures:

• Clean #57 / 3/4 in stone — 2,700 lb/cu yd (1.35 ton). The fines are screened out, so it drains but will not compact tight.
• Crusher run / #411 — 2,850–3,100 lb/cu yd (≈1.48 ton). Stone dust fills the voids, which is why it compacts and why it is heavier.
• Pea gravel — 2,800–3,200 lb/cu yd. Limestone-based runs at the top of that range, granite-based at the bottom.
• River rock — quoted anywhere from 2,500 to 3,500 lb/cu yd. Larger, rounder stone traps more air, so a yard of 5 in cobble can weigh less than a yard of pea gravel. This is the one figure worth getting from your own supplier.

Quarries quote dry weight. After a week of rain the same volume on your truck weighs 5–10% more.

What this does not include

• Geotextile fabric under the base, which is what stops the stone migrating into soft subgrade.
• The surface layer. A driveway is usually 4–6 in of base plus about 2 in of a finer top course — run the calculator twice.
• Pipe displacement. For a French drain, the pipe occupies part of the trench and has to come off the volume.