Gravel Calculator

How to Use the Gravel Calculator

The awkward thing about ordering gravel is that you measure a hole and the supplier sells you a weight. Everything on this page exists to bridge that gap honestly, including being clear about how much slack there is in the middle of it.

1. Measure the area to be covered. Length and width in feet for a rectangular drive or path. For anything irregular, break it into rectangles and add the results, or use the square footage calculator first.
2. Set the depth in inches. Two inches suits a decorative path, three to four a walked-on surface, and four or more a driveway carrying cars. Base layers under paving run deeper still.
3. Choose the material. Each carries its own bulk density, and that density is what converts your volume into the tonnage a supplier will quote against.
4. Add a price per ton and a truck size. These turn the tonnage into a cost and a number of deliveries, which is usually the figure that decides the job.

The whole calculation runs in your browser. Nothing about your driveway is transmitted anywhere, and the page needs no connection once loaded.

Gravel Volume and Tonnage Formulas

Volume first, then weight. The volume is simple geometry; the weight depends on a density figure that is genuinely uncertain, and pretending otherwise is how people end up a ton short.

Density is the loose figure, measured as the material sits in a heap. It is not the compacted density, which is higher, and it is not the solid density of the rock itself, which is much higher — roughly 165 lb per cubic foot for limestone with no air between the pieces. What you are buying is stone plus the gaps.

Those gaps are why the same load can weigh differently on different days. Rain fills the voids, and water at 62.4 lb per cubic foot is not weightless. A soaked pile of crushed stone can run five to ten per cent heavier than a dry one, and you are paying by the ton.

Example

Worked example one: a 40 ft by 12 ft driveway, 4 inches deep. The area is 480 square feet. Four inches is 0.3333 feet, so the volume is 480 × 0.3333 = 160 cubic feet, or 160 ÷ 27 = 5.93 cubic yards.

At crushed stone's 100 lb per cubic foot the raw volume would weigh 160 × 100 = 16,000 lb, or exactly 8 US tons. But gravel settles, so the standard 5% allowance goes on first: 160 × 1.05 = 168 cubic feet, which is 6.22 cubic yards.

That is 168 × 100 = 16,800 lb, or 8.40 US tons and 7.62 metric tonnes. At $45 a ton delivered the material costs $378, and at ten cubic yards a truck it is 0.62 of a load — one delivery, part full, and you will very likely pay for the whole trip.

The allowance is not padding. Unbound gravel compacts under traffic, and a drive that measured four inches on delivery day measures three and a half by the spring. Ordering the raw 8 tons rather than 8.40 leaves you finishing the last few square feet from a wheelbarrow.

Worked example two: the same hole, different stone. Nothing about the geometry changes — it is 168 cubic feet whatever you fill it with. But crusher run base at 125 lb per cubic foot weighs 168 × 125 = 21,000 lb, which is 10.50 tons. Limestone chippings at 95 lb per cubic foot weigh 15,960 lb, or 7.98 tons.

That is a spread of 2.52 tons — nearly a third — for one identical excavation. At $45 a ton it is a $113.40 difference, and it is entirely invisible if you order by weight without checking which material the density figure belongs to.

Ordering: Volume Is Exact, Weight Is Not

Order by volume and check by weight, not the other way round. The cubic-yard figure is what your excavation actually holds and it is close to exact. The tonnage is a conversion through a density that varies with moisture, grading and how the pile was loaded, so treat it as accurate to within a few per cent rather than to the pound.

Depth deserves more thought than area, because it is the dimension people guess at. Doubling a driveway's depth doubles the material and the cost, while widening it by a foot on each side adds far less. A drive laid too thin ruts under the first wet winter, so this is not the place to economise.

The truckload figure matters more than it looks. Deliveries are priced per trip as much as per ton, so a job needing 0.59 of a load and a job needing 1.05 loads have very different delivery bills for a small difference in material. Rounding a job slightly down to fit one load, or slightly up to make a second load worthwhile, is a real saving.

For a driveway specifically, the usual build-up is a compacted sub-base of crusher run four to six inches deep, then a two-inch decorative top layer. Those are two different materials at two different densities and two different prices, so run the calculator twice rather than treating the whole depth as one order.

The sand calculator covers bedding sand under pavers, and the concrete calculator handles the slab if you decide against loose stone entirely.

Five Reasons the Delivery Differs

Five reasons the delivered weight differs from the calculated one.

Moisture. The single biggest factor. Voids in a loose pile fill with water, and a saturated load can weigh five to ten per cent more than the same stone dry. You pay for that water by the ton and it drains away into the ground.

Compaction. Loose gravel settles under its own weight and much further under traffic, typically by ten to twenty per cent for an unbound base. The small waste allowance here covers spillage and edges; a properly compacted sub-base needs more than that, and the depth should be specified as the finished compacted depth.

Grading. Uniform, single-size stone packs less densely than a well-graded mix where small pieces fill the gaps between large ones. That is exactly why crusher run is heavier per cubic foot than pea gravel, and why it makes a better base and a worse surface.

Edge losses. Gravel without an edge restraint migrates outwards and into the surrounding ground, particularly on a slope. A drive without kerbing or edging loses material every year and needs topping up, so the first order is not the last one.

Supplier conventions. Some yards quote in short tons, some in metric tonnes, some by the cubic yard, and the difference between a short ton and a tonne is 10%. Confirm which unit a quote uses before comparing two of them, because the cheaper price per unit is not always the cheaper delivery.