The calculator turns the size of your area and the depth you want into an order: tons for a bulk delivery, loose cubic yards for a yard that sells by volume, and a bag count for small jobs. It weighs each stone separately and adds extra only where the stone packs down, which is where flat-rate estimates go wrong.
How to use the gravel calculator
Choose the project, measure each area in feet, pick the stone and its finished depth, then decide how much extra to add.
- Pick the project. Decorative bed, Path or patio and Driveway each load a sensible set of layers. A decorative bed is a single layer, which also suits any other one-layer job; a path or patio gets a base layer and a surface layer; a driveway gets a thick base under a surface course. Every stone and depth stays editable.
- Measure each area. Enter a rectangle as length and width, a circle as its diameter, a triangle as its three sides, or type a known area. Add as many areas as you need: an L-shaped path is two rectangles, and a round sitting area at the end of it is a third shape. Switch to meters and centimeters if your tape reads metric.
- Set the stone and the finished depth. Depth means the thickness you want to walk or drive on, after compaction for the stones that compact. The calculator adds the stone that packing removes.
- Choose the extra. Pick none, 5%, 10% or 15% for waste and uneven ground. Ten percent is the default.
- Add a price if you have one. Enter your supplier's price per US ton or per cubic yard for a material estimate before delivery charges. The price stays per US ton or cubic yard in metric mode too.
The result gives tons to order, loose cubic yards (or cubic meters and tonnes), a weight range for the stone you chose, and either a bag count or the finished volume on the ground. Two-layer jobs show each layer on its own line, and single-layer jobs also show how far one ton goes at your depth. If the stone is not on the list, choose Other and enter the tons per cubic yard printed on your supplier's ticket or website. Other adds no packing allowance, so for a stone that compacts, enter about 1.3 times the finished depth (1⅓ times for decomposed granite or stone dust).
The gravel formula, worked through
Gravel is ordered by volume or weight, and both come from three numbers: area, depth and the weight of the stone.
- Cubic feet = square feet × depth in inches ÷ 12.
- Cubic yards = cubic feet ÷ 27, or square feet × inches ÷ 324 in one step.
- Tons = cubic yards × the stone's tons per cubic yard.
A cubic yard is exactly 27 cubic feet, because a yard is exactly 3 feet. For a circle, the area is 3.1416 × half the diameter × half the diameter. In metric, square meters × centimeters ÷ 100 gives cubic meters; one cubic yard is 0.7646 m³ and one US short ton is 0.9072 metric tonne (907 kg).
Here is the job the calculator opens with: a decorative bed 20 by 10 feet (6.1 × 3.0 m), covered with river rock 3 inches (7.6 cm) deep, with 10% extra.
- Area. 20 × 10 = 200 square feet (18.6 m²).
- Finished volume. 200 × 3 ÷ 12 = 50 cubic feet (1.42 m³). River rock does not compact, so nothing is added for packing.
- Extra. 50 × 1.10 = 55 cubic feet.
- Cubic yards. 55 ÷ 27 = 2.04 cubic yards (1.56 m³) of loose stone to order.
- Tons. 2.04 × 1.3 = 2.6 tons (2.4 tonnes).
- Bags. 55 ÷ 0.5 = 110 half-cubic-foot bags.
The calculator also shows 2.2 to 2.8 tons as the weight range, because river rock from different quarries and in different sizes weighs more or less per yard. If your supplier sells by the yard, order the 2.04 cubic yards and the weight takes care of itself.
How much gravel weighs, and how far a ton goes
Most clean stone weighs a little over a ton and a quarter per loose cubic yard. Stone with fines weighs more, because the fine particles fill the gaps.
| Stone | Tons per cubic yard | Range | Extra to compact |
|---|---|---|---|
| Pea gravel | 1.3 (1,543 kg/m³) | 1.25–1.4 | None |
| Clean crushed stone (#57) | 1.3 (1,543 kg/m³) | 1.2–1.4 | None |
| River rock (½–1½ in) | 1.3 (1,543 kg/m³) | 1.1–1.35 | None |
| Crusher run / road base | 1.4 (1,661 kg/m³) | 1.25–1.5 | +30% |
| Decomposed granite | 1.35 (1,602 kg/m³) | 1.25–1.55 | +33% |
| Stone dust (screenings) | 1.4 (1,661 kg/m³) | 1.3–1.67 | +33% |
Loose, as-delivered weights. Rock type, stone size and moisture move a load within the range.
Five things move the weight of a load:
- Rock type. Trap rock is denser than limestone or granite, and sandstone is lighter, so the same size of crushed stone weighs differently from quarry to quarry.
- Stone size and shape. Big rounded river rock leaves big voids, so a yard of 6-inch (15 cm) cobble weighs less than a yard of half-inch pebbles.
- Fines. Dense-graded base, decomposed granite and stone dust pack small particles into the voids, which adds weight per yard.
- Water. Highway-department weight tables are for dry stone, and a load carrying 3 to 7% moisture weighs about 3 to 7% more. The calculator's figures are as-delivered estimates; the clean-stone figure sits at the top of the dry range for granite and limestone to allow for that water.
- Loose or compacted. Compacted dense-graded base weighs about 1.85 tons per cubic yard dry, in place. The calculator reaches nearly the same figure from the other direction: loose base at its loose weight plus a packing allowance works out to 1.82 tons for every finished cubic yard. Both are dry figures, so expect a damp load to weigh a few percent more on the scale.
For clean stone, enter your supplier's own tons-per-yard figure under Other. Other adds no packing allowance, so for base, decomposed granite or stone dust either keep the listed stone and compare its weight range with the supplier's figure, or enter about 1.3 times your finished depth.
A ton covers less ground the deeper you spread it: double the depth and the area halves. Stones that compact cover less, because part of each ton fills the voids as it packs.
| Stone | 2 in (5.1 cm) deep | 3 in (7.6 cm) deep | 4 in (10.2 cm) deep |
|---|---|---|---|
| Pea gravel | 125 sq ft (11.6 m²) | 83 sq ft (7.7 m²) | 62 sq ft (5.8 m²) |
| Clean crushed stone (#57) | 125 sq ft (11.6 m²) | 83 sq ft (7.7 m²) | 62 sq ft (5.8 m²) |
| River rock (½–1½ in) | 125 sq ft (11.6 m²) | 83 sq ft (7.7 m²) | 62 sq ft (5.8 m²) |
| Crusher run / road base | 89 sq ft (8.3 m²) | 59 sq ft (5.5 m²) | 45 sq ft (4.1 m²) |
| Decomposed granite | 90 sq ft (8.4 m²) | 60 sq ft (5.6 m²) | 45 sq ft (4.2 m²) |
| Stone dust (screenings) | 87 sq ft (8.1 m²) | 58 sq ft (5.4 m²) | 43 sq ft (4 m²) |
Area one ton covers at each finished depth, before any extra. Compacting stones are measured after compaction.
How deep to lay gravel for each project
Decorative stone goes down in one layer of 1 to 4 inches (2.5 to 10 cm); paths, patios and driveways need a compacted base under a separate surface layer. Whatever the job, make each layer at least twice as thick as the largest stone in it, so 1-inch (2.5 cm) stone needs a 2-inch (5 cm) layer at minimum. A thinner layer leaves stones rolling loose with bare patches between them.
| Project | Layer | Stone | Finished depth |
|---|---|---|---|
| Decorative bed | Gravel | River rock (½–1½ in) | 3 in (7.6 cm) |
| Path or patio | Base | Crusher run / road base | 4 in (10.2 cm) |
| Surface | Decomposed granite | 3 in (7.6 cm) | |
| Driveway | Base | Crusher run / road base | 8 in (20.3 cm) |
| Surface | Crusher run / road base | 4 in (10.2 cm) |
The calculator's starting depths for each project; adjust them for your stone size, soil and traffic.
Decorative beds and rock mulch. A 1-inch layer of small stone controls weeds well in a bed that starts clean. Where weeds are persistent, 4 inches (10 cm) is the depth that keeps most of them down, and the stone should be smaller than about ½ inch (13 mm) to act as mulch. A 3-inch (7.6 cm) layer of gravel mulch can also multiply how much rain soaks into the soil.
Paths, patios and seating areas. The surface is a fines-rich stone such as decomposed granite or stone dust, laid in one pass 4 inches (10 cm) loose and compacted to 3 inches (7.6 cm). Under it goes 2 to 6 inches (5 to 15 cm) of compacted dense-graded base; a firm, well-drained existing path may need little or none. Give the surface a cross-slope of about ¼ inch per foot (2 cm per meter, roughly 2 percent) so water runs off. Path specifications range from 1 to 4 percent, and the gentler end is easier to walk on.
Driveways. Build 8 to 12 inches (20 to 30 cm) of compacted base, then a surface course compacted to 4 to 6 inches (10 to 15 cm). A dense-graded surface placed 6 inches (15 cm) loose finishes near 4½ inches (11.4 cm); placed 8 inches (20 cm) loose, it finishes at 6 inches (15 cm). Crown the drive so it falls about ½ inch per foot (about 4 cm per meter, a 4 percent slope) from the center to each edge.
French drains. Use the Decorative bed project, switch the stone to clean crushed stone, and enter the trench length and width as the area and the trench depth minus the cover layer as the depth. Line the trench with lightweight non-woven geotextile, keep a steady fall to the outlet, and put the larger stone at the bottom: clean stone 2 to 4 inches (5 to 10 cm) across drains best there. Wrap the fabric over the top of the stone.
Finish with about 6 inches (15 cm) of path material on a footpath, or at least 12 inches (30 cm) of cover under a ditch or a driveway. Size that topping as a second calculation.
Paver patios. Base depth depends on the paver and the load, so size a paver patio with the paver calculator rather than a generic gravel depth. For a gravel shed pad, use the Decorative bed project with crusher run at the base depth the shed maker specifies.
Choosing the right stone for the job
Use clean stone where water has to drain away and stone with fines where people walk or drive; the two do opposite jobs.
Clean, open-graded stone such as #57 and pea gravel has open voids and no fine particles. Water runs straight through it, which makes it the stone for drains and decorative beds, but it never binds into a crust. Used as a path or driveway surface, it stays loose and ruts under tires.
Dense-graded stone, sold as crusher run, road base or 2A modified, runs from coarse pieces down to dust. It compacts into a firm layer that sheds water, so it makes a good base and drive surface and a poor drain. Never spread a fines-rich surface directly over open-graded stone: the fines wash down into the gaps and the surface loosens.
| Stone | Size | Fines | Best use |
|---|---|---|---|
| #57 crushed stone | 1½ in to 3/32 in | None | French drains and other buried drains |
| Pea gravel | About ⅜ in, rounded | None | Decorative beds |
| Stone dust, screenings (#10) | Under ⅜ in | High | Path and patio surfaces |
| Decomposed granite | ⅜ in to fines, weathered granite | High | Path, patio and drive surfaces |
| Dense-graded base (2A modified, ABC) | 2 in to dust | Well graded | Base under paths and drives; drive surface |
In the AASHTO size numbers, lower means larger stone and #57 blends sizes 5 and 7; "modified" means fines have been blended in.
Names change by region. The same dense-graded material is called 2A modified in Pennsylvania, ABC (aggregate base course) in Arizona, crushed surfacing in Washington and dense graded base in Wisconsin. Ask the stone yard for its dense-graded base with fines, whatever it calls it.
Rock mulch does not decompose, so it is best kept for permanent plantings such as foundation shrubs. In wildfire country it is the best mulch for the zone right around a house, though it carries more heat into the soil and into nearby walls than wood chips.
Keep it away from acid-loving shrubs such as blueberries, because the rock may add alkaline elements to the soil. Stone also reflects sun and makes beds very hot in summer, so avoid it against sunny walls. Around those plants a wood mulch works better; the mulch calculator sizes that order.
No reliable published weight exists for marble chips or lava rock, and lava rock is porous and far lighter than dense stone. Buy them by the bag or the cubic yard, or enter your supplier's figure under Other.
Why compacting stone needs extra, and how much to add
Stone with fines shrinks when it is compacted, so you order more loose stone than the finished depth. Clean stone does not compact into a dense mass and gets no allowance.
Packing squeezes air out of the gaps between particles. Dense-graded base needs about 1.3 times its finished volume in loose stone. Decomposed granite and stone dust need about a third more, since they go down 4 inches (10 cm) loose to finish at 3 inches (7.6 cm).
Pea gravel, #57 and river rock settle only slightly under tamping and traffic. Under a driveway or a tamped patio base, choose the 15% extra for them. A road-base shrink factor on clean stone would buy about 30% more stone than the space holds.
Take a path 3 by 40 feet (0.9 × 12.2 m), or 120 square feet (11.1 m²). It gets a 4-inch (10 cm) crusher run base under a 3-inch (7.6 cm) decomposed granite surface, with 10% extra:
- Base. 120 × 4 ÷ 12 = 40 cubic feet finished. × 1.3 for packing = 52 cubic feet. × 1.10 = 57.2 cubic feet, or 2.12 cubic yards and about 3.0 tons.
- Surface. 120 × 3 ÷ 12 = 30 cubic feet finished. × 4 ÷ 3 for packing = 40 cubic feet. × 1.10 = 44 cubic feet, or 1.63 cubic yards and 2.2 tons.
- Order. 3.75 cubic yards (2.87 m³) in all, about 5.2 tons (4.7 tonnes).
The 10% default matches the waste allowance highway engineers add when stone is stockpiled before spreading. On soft ground or a busy driveway, choose 15%. That raises the base to about 1.5 times its finished volume, the top of the measured range for dense-graded base. It also adds 15% to the surface layer.
Bags or bulk
Bags suit small beds and touch-ups up to about a pallet, 1.17 cubic yards (0.89 m³); beyond that a bulk load is easier to buy and to move. The calculator keeps counting bags up to 3 cubic yards (162 bags) so you can compare the two, and shows only bulk figures above that.
Decorative stone such as pea pebbles, river pebbles, marble chips and lava rock is sold by volume in half-cubic-foot (14 L) bags, 63 to a pallet. Fifty-four of them make a cubic yard, and a full pallet holds 31.5 cubic feet. Plain all-purpose gravel is sold by weight in 50-pound (22.7 kg) bags, 56 to a pallet, which puts 2,800 pounds (1,270 kg) on one pallet. Those bags do not state a volume, so count each as roughly half a cubic foot.
What the stone will cost
The material bill follows the order: the stone, the area and above all the depth. Going from 3 to 4 inches adds a third to a layer, and stone that compacts costs more per finished inch because you buy about 1.3 times its finished volume.
Bulk stone is priced by the ton or by the cubic yard. If one supplier quotes per ton and another per yard, multiply the per-ton price by the stone's tons per cubic yard before comparing. For bagged stone, multiply the price of one half-cubic-foot bag by 54 to get its price per cubic yard. The price you enter in the calculator covers the stone alone, so ask the yard for its delivery charge and any minimum load before you compare quotes.
Preparing the ground before the stone goes down
Gravel can go straight onto soil only in a decorative bed. Paths and driveways need the sod and topsoil out, a firm subgrade and a compacted base, or the stone sinks and turns to mud.
- Strip sod and topsoil. Remove grass, roots and soft organic soil to the depth of the layers you planned, so the stone rests on firm subsoil. The cubic yard calculator gives the volume of soil coming out, for haul-away.
- Lower beds below grade. Dig a decorative bed about 3 inches (7.6 cm) below the surrounding lawn or paving so the stone finishes level instead of spilling over, and make sure the bed does not collect runoff.
- Shape for water. Grade the subsoil to the same cross-slope or crown the finished surface will have, so water leaves every layer.
- Compact the subgrade. Firm ground under the base keeps the finished depth from sinking. Hand-tamp small areas; for paths and drives use a powered plate compactor or a small roller.
- Separate soft soil. Soil with about 20% silt or clay behaves like mud when wet and pumps up into stone. Lay a non-woven geotextile with openings no larger than 0.3 mm (0.01 in) on those soils under paths, patios and drives. Skip woven plastic and black plastic in planted beds, where they cut air and water to the roots.
- Set edging. Install edging before the stone so it holds the layer to its full depth at the margins.
- Spread and compact in lifts. Spread base in lifts of 3 inches (7.6 cm), or up to 4 inches (10 cm) with a plate compactor of about 4,000 lb force or more; dampen each lift and compact it before the next. Lay the 4-inch (10 cm) loose surface of decomposed granite or stone dust in one lift and compact it once, because reworking it in several passes separates the coarse pieces from the fines.
Mistakes that cost the most
- Entering a loose depth for compacting stone. The calculator already adds packing allowance, so typing 5 inches (13 cm) for a 4-inch (10 cm) crusher run base orders about a quarter more stone than you need.
- Trusting one weight for every stone. A single 1.5-tons-per-yard factor overstates clean stone by about 15%; pick the stone, then check your supplier's factor.
- Ordering before the layers are settled. A drive surface without its base, or a path surface laid straight on soil, breaks up and gets bought twice.
Before you order, sketch where the paths, beds and drive will sit in Sow's garden design studio, and measure from the plan.