Gravel Calculator

How to use the gravel calculator

Measure the area in feet at its longest and widest points. For paths and curved runs, treat each straight-ish stretch as its own rectangle, run the calculator per section, and add the results — a 40 ft winding path that averages 3 ft wide is simply 40 × 3, because the meander does not change the area.

Round up to the nearest half foot; gravel is forgiving and the truck does not deliver in teaspoons. If the ground is uneven or you are filling an existing depression rather than laying a layer on flat grade, probe the depth in several places and enter the average rather than the deepest point, or you will pay for a hole you do not have.

Depth depends entirely on what the surface has to do. Two to three inches suits decorative ground cover and weed-suppressing layers over fabric, and three inches is the usual working depth for a walkway.

Anything that carries vehicles is a different animal: a residential drive is normally built up in two or three compacted lifts of progressively finer stone rather than one deep pour, because eight loose inches dumped in a single go stays soft and ruts in the first wet week.

Calculate each lift separately at the compacted setting and add them, and size the build-up against a local spec — frost depth and subgrade soil change the answer far more than any calculator can.

The advanced density setting converts volume to weight, because bulk suppliers quote and sell by the ton as often as by the yard. The default of 1.4 tons per cubic yard sits inside the range you get by working from the average specific gravity FHWA reports for waste rock, about 2.65, at realistic void fractions — roughly 1.2 to 1.45 tons per cubic yard for typical crushed stone and pea gravel.

Use your quarry’s own published figure whenever they give one, since gradation, parent rock, and moisture all move it. Then plan for the pile before it lands: a cubic yard is well over a ton, and where the driver tips it is where it stays until you move it barrow by barrow. This is a shopping estimate, not a contractor’s takeoff.

Loose fill or compacted base: which setting?

The coverage-type select matters more than it looks. Loose fill is gravel that stays roughly the volume you poured: decorative rock, French-drain fill, top layers over fabric. Compacted base adds 15 percent because stone packed with a plate compactor or roller consolidates, and the same excavation swallows noticeably more material than its open volume suggests.

Use compacted for anything bearing load — paver and patio bases, shed pads, driveway lifts, post backfill — and loose for anything decorative or drainage-related. Getting this wrong in the cautious direction costs you a wheelbarrow of surplus; getting it wrong the other way stops a paver job halfway through with the base one inch shy of grade.

The formula, worked line by line

Underneath the compaction factor and the tonnage conversion, this is the same volume calculation every bulk material uses: area multiplied by depth. The friction comes from the units. You measure the area in feet, choose the depth in inches, order by the cubic yard from a landscape yard, and get quoted by the ton at a quarry, so three conversions sit between the tape measure and the invoice.

Divide the depth by 12 to turn inches into feet so the multiplication yields cubic feet. Divide by 27 to reach cubic yards, since a yard is three feet on every side. Multiply by the compaction factor if the layer will be packed, and multiply the yards by a density in tons per cubic yard if your supplier sells by weight. Each step is trivial; missing one is what produces an order that is out by a factor of twenty-seven.

cubic feet = length ft × width ft × (depth in ÷ 12) × compaction factor
compaction factor = 1.00 loose fill · 1.15 compacted base
cubic yards = cubic feet ÷ 27
tons = cubic yards × density in tons per cubic yard

Where the 1.4 default comes from: FHWA reports an average specific gravity of about 2.65 for waste rock, with a range from 2.4 to 3.6 depending on the mineral constituents. Solid stone at 2.65 weighs about 165 lb per cubic foot, but a pile of stone is mostly stone and partly air.

At a realistic 35 to 45 percent voids that works out to roughly 91 to 107 lb per cubic foot, or about 1.23 to 1.45 tons per cubic yard. The tool defaults to 1.4 and lets you set anything from 1.2 to 1.7, so a supplier’s published figure always wins over ours.

If you are buying by the ton while thinking in yards, remember that the conversion runs both ways: at 1.4 tons per cubic yard, one ton is about 0.71 cubic yards, which covers roughly 77 square feet at 3 inches deep. Comparing a per-ton quote against a per-yard quote without doing that conversion is how two identical loads look like different prices.

Questions people ask