Gravel calculator

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, and it is why this page asks whether the stone gets compacted rather than treating depth as the whole question. Take the finished depth you want, convert it straight to volume and order that, 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.

When the tonnage will be wrong

Two of the four inputs above are conventions rather than measurements, and the tons output inherits everything that is loose about them:

• The dropdown carries one weight per stone; reality carries a range. River rock alone is quoted across a thousand pounds a cubic yard, and the figure that prices your ticket belongs to one quarry and one gradation. Every ton here moves with it.
• Weight per yard is quoted three different ways — stone poured loose into a measure, stone as delivered and settled, and stone compacted in place. They are not the same number, and this page uses the loose one throughout. When you ask your supplier for a density, ask which of the three you are being given.
• The stone and the compaction allowance are two separate questions here, and nothing couples them. Leave the allowance at the dense-graded default while picking pea gravel or river rock and the page prices a quarter more stone than the bed will hold, because rounded stone is not compacted at all. The pairing is yours to make: decorative stone goes with No — loose decorative stone.
• The compaction allowance is a convention, not a prediction. How far a lift actually settles depends on the lift thickness, the moisture in the stone, the machine and the ground underneath. On soft subgrade some of the first load disappears into the soil, and no percentage on this page covers that.
• It assumes a flat area at one finished depth. A crowned driveway, a swale, a path that thins at the edges, or ruts you are filling before you start are all extra volume, measured separately.
• Nothing here says the depth is right. How much base your traffic and your soil need is a design question, and it is the one that decides whether the driveway is still flat in three years.

The coverage-per-ton figure is useful for checking a per-ton quote and nothing more: it converts a weight to an area at the loose density, so it describes the pile on the ground, not the finished surface after a plate has been over it.