Gravel: cubic yards versus tons
One supplier quotes you a price per ton, the next quotes per cubic yard, and you are trying to work out which is cheaper for the same pile of stone. They measure different things, weight against volume, and converting between them takes one number that changes with the stone.
Gravel calculator
How much gravel do you need?
Working out a whole yard rather than one bed? Sketch it to scale in the planner and every area is measured, costed and totalled together.
Start with volume
Whatever the supplier quotes, work out your volume first. Same formula as any other material sold by depth:
cubic yards = (square feet × depth in inches) ÷ 324
A 4 foot wide path running 60 feet is 240 square feet. At 3 inches deep that is (240 × 3) ÷ 324 = 2.2 cubic yards.
Then convert to weight
tons = cubic yards × tons per cubic yardcubic yards = tons ÷ tons per cubic yard
That middle number is density, and it is the whole reason the two units do not line up neatly. These are the figures the planner uses:
| Material | Tons per cubic yard | A 2.2 yard path weighs |
|---|---|---|
| Gravel / crushed stone | 1.4 | 3.1 tons |
| Decomposed granite | 1.5 | 3.3 tons |
| River rock | 1.4 | 3.1 tons |
Treat those as planning figures, not physics. Ask your supplier for theirs before a large order. On ten yards, a density that is off by 0.1 moves the bill by a full ton.
Why density moves
- The rock itself. Granite, limestone, basalt and river stone differ in density before anything is stacked. Two piles graded identically, cut from different quarries, will not weigh the same.
- Fines. This is the big one. Crusher run and road base carry stone dust that fills the gaps between the larger pieces, so a well-graded product weighs noticeably more per yard than a single-size stone cut from the same rock.
- Shape. Angular stone interlocks, which is why it stays put underfoot and why base courses are built from it. That interlock buys stability rather than weight, though. Angular pieces bridge against each other and leave slightly more air than rounded ones do, which is why the table above gives crushed stone and river rock the same figure.
- Not the stone size, though. A yard of pea gravel and a yard of 2 inch stone of the same rock weigh about the same. Bigger pieces leave bigger gaps, but the proportion of air stays much the same, so it is the spread of sizes that moves the weight, not the size itself.
- Moisture. Wet stone can run 10% heavier than the same stone dry. If you are buying by weight after three days of rain, you are paying for water.
That last one cuts both ways, and it is the practical argument for buying by volume where you have the choice: a cubic yard is a cubic yard whatever the weather did.
How deep
| Use | Depth | Notes |
|---|---|---|
| Decorative beds | 2 in | Over fabric, mainly for looks |
| Walking paths | 2–3 in | Deeper feels loose underfoot |
| Driveway surface | 4 in | On top of a compacted base, not on bare soil |
Loose stone travels, so a path or a decorative bed wants edging holding its shape. Without it the stone spreads into the lawn a little every year, the layer gets thinner, and you end up topping up a path that never actually wore out.
A driveway is two layers, not one. The surface stone sits on a compacted base course, and the base is what actually carries the load. A thick layer of pretty stone straight onto soil will rut the first time something heavy parks on it.
Order extra for compaction
Crushed stone with fines in it compacts by roughly a fifth once it is rolled or plate tamped. So a finished 4 inch layer starts life about 5 inches loose, and your order should be based on the loose figure:
order ≈ compacted volume × 1.25
Clean rounded stone like pea gravel and river rock barely compacts at all, so skip the allowance there and just add the usual 5–10% for spillage and uneven ground.
The same stone doing the same job under a paver patio wants the same treatment, and there the compaction is not optional at all: a base that settles under pavers takes the surface down with it.
Before you call the supplier
- Know your cubic yards. You can convert to tons at the counter; you cannot convert if you never worked out the volume.
- Ask which unit the quoted price is in, and ask their density figure for that specific stone.
- Ask about minimums. Many yards will not deliver under 1 ton or 1 cubic yard, which makes a small job disproportionately expensive.
- Ask where the truck can tip. Gravel is far heavier than mulch and moving it twice by barrow is a long afternoon.
Work out your volume in the planner
Paint the path or the drive, set the depth, and the totals panel gives you square feet, cubic yards and tons side by side, so whichever unit the supplier quotes in, you already have the number.