Decomposed Granite Calculator — South Dakota

This calculator turns the size of your project into the material you need to order. Decomposed granite, or DG, is weathered granite ground down to fines. You spread it over pathways, patios, driveways, xeriscape beds, and under-tree areas. The tool sizes the loose material for any of these jobs.

The estimate starts with two inputs. The first is the area you plan to cover. The second is the depth you plan to spread. The calculator multiplies area by depth to reach a volume. It reports that volume in cubic yards and the weight in tons.

Depth is entered in inches, so the tool converts inches to feet first. A 3-inch layer becomes 0.25 feet. It then multiplies the area by that depth to get cubic feet. It divides the cubic feet by 27 to convert to cubic yards. Twenty-seven cubic feet fill one cubic yard.

Next the tool converts volume to weight. Decomposed granite weighs about 1.4 tons per cubic yard. The real value runs from 1.3 to 1.5 tons, depending on moisture and how fine the product is. The calculator multiplies your cubic yards by 1.4 to give a working tonnage.

The last step adds a compaction allowance. The default is 10 percent. Decomposed granite is placed in lifts and packed down, so loose material settles below its poured depth. The allowance covers that settling plus spillage and uneven ground.

The result gives you both cubic yards and tons. Bulk yards sell DG by weight, so the ton figure is what your supplier needs. The cubic yard figure lets you cross-check a plan that talks in volume. Enter your area and depth to see your totals.

Depth is the biggest lever on how much you order, and the right depth depends entirely on what the surface has to do. Getting it right before you calculate keeps the order honest.

Most paths and patios use about 2 to 3 inches of decomposed granite. This depth gives a firm, walkable surface once packed. Spread it in lifts of an inch or two and compact each lift before adding the next. A single deep lift will not pack down fully at the bottom.

Use the shallower end of the range over a firm, stable subgrade. Use the deeper end where the ground is soft or where foot traffic is heavy. The finished depth is what you want after compaction, not the loose depth you pour. Plan for the packed number and let the allowance cover the settling.

Driveways ask more of the material. A DG driveway carries vehicle weight, so it needs a deeper section built over a compacted base. Plan a crushed-stone base first, then the decomposed granite over the top. The base spreads the load and keeps the surface from rutting under tires.

Xeriscape beds and under-tree areas are different again. Here the DG is a top dressing, not a traffic surface. A 2-inch layer covers the soil, holds moisture, and gives a clean earth-tone finish. You do not need to compact a decorative layer as hard as a path.

Set your depth by the job before you read the tonnage. A path, a driveway, and a mulch bed each call for a different number. Enter the depth that matches your surface, then trust the result the tool returns.

Decomposed granite is sold two ways, by the ton and by the cubic yard. Knowing both units keeps your order clear and lets you check any quote.

A cubic yard measures volume. It is a block 3 feet on every side, which equals 27 cubic feet. A ton measures weight. To move between the two, you use the density of the material. Density is the weight packed into one cubic yard.

This calculator handles the conversion for you. It finds the cubic yards from your area and depth, then multiplies by density to reach tons. Decomposed granite runs about 1.4 tons per cubic yard. So a project that needs 5 cubic yards needs about 7 tons.

Density is not a fixed number. Decomposed granite ranges from about 1.3 to 1.5 tons per cubic yard. Moisture raises the weight, since damp fines weigh more than dry ones. A finer, more compacted product also packs heavier. The tool uses 1.4 as a solid planning value.

Why report in tons at all? Bulk material is weighed on a truck scale at the yard. The delivery ticket lists tons. A tonnage estimate matches that ticket, so you can compare what you paid for against what arrived on site.

If your supplier sells by the cubic yard instead, the tool still works. Take the reported tons and divide by 1.4 to get cubic yards back. Either unit describes the same pile of material. The point is to order the right amount without guessing. Ask your yard which unit they quote in, then match your order to it. A clear unit stops a short delivery.

Decomposed granite does not stay as loose as it arrives. When you run a plate compactor over it, the fines lock together and the layer shrinks. This is compaction, and it is what makes a DG surface firm enough to walk on.

Because the material settles, loose DG drops below its poured depth. Plan the finished depth first, then order enough loose material to reach that depth after packing. If you order only for the finished depth, you will come up short once the compactor runs.

The calculator adds a compaction allowance to cover this. The default is 10 percent. The same allowance also covers uneven subgrade, spillage while spreading, and the material lost at the edges of the work. On a rough or sloped site, raise the allowance.

Compact in lifts, not all at once. Spread the DG in layers of an inch or two, then pack each layer before adding the next. Lightly wet each lift before you compact it. Damp fines bind together far better than dry ones and hold a firmer surface.

A thick single lift does not pack fully at the bottom. The lower part stays loose and the surface sinks later. Thin lifts, each compacted, build an even, stable path that holds its shape through the seasons.

Add a bit more if your ground is soft. Soft soil pushes up into the DG and steals depth from the layer. When you are unsure, order slightly long. A small surplus of decomposed granite is far cheaper than a second delivery and a stalled job. Keep the allowance on and round your order up to the next practical amount.

Once you know your tonnage, plan the delivery. Bulk decomposed granite arrives by dump truck. One standard dump truck holds about 10 to 14 tons. Your total tells you how many truckloads the job needs.

A small path or patio may need only a few tons. That fits in a single load with room to spare. A driveway or a large xeriscape project can run past one truck. If your total climbs above the truck limit, expect more than one delivery, or a larger vehicle. Ask your supplier what their trucks carry.

Think about where the truck will dump. Bulk DG drops in a large pile. Pick a spot close to the work but clear of the area you are grading. A pile on the path footprint blocks your spreading. A pile far from the work means a long wheelbarrow haul.

Protect the drop area. Dumping fine granite on a lawn leaves ruts and stains, and the fines wash into the grass. A tarp or a sheet of plywood keeps the pile off the surface and makes cleanup faster. It also stops rain from carrying the fines away.

Moisture matters with DG. The fines pack and bind best when they are slightly damp. A pile that sits out in heavy rain gains weight and can wash out of shape. A pile that bakes dry is harder to compact. Cover the pile if it will sit for a while.

Check the weighed ticket when the truck arrives. It lists the tons delivered. Compare that against your estimate. A close match confirms the order is right. Have your tools and helpers ready, since bulk material sits in the open until you spread it.

A lasting decomposed granite surface starts with the ground under it. The tonnage the calculator gives you assumes the area is graded to the right depth across the whole footprint. If the subgrade is uneven, your numbers will not fit and the surface will not hold.

Start by marking the shape and setting the depth. Strip the sod, roots, and loose topsoil from the area. These soft materials rot and settle, which lets the DG sink in patches. Grade the exposed soil smooth, then compact it. A firm subgrade keeps the finished path from dishing under traffic.

Set a slight slope for drainage. The surface should shed water rather than pool it. A small fall across the path carries rain to the edges and away. Standing water softens the fines and cuts channels through the DG over time.

A path or patio can sit on compacted soil for foot traffic. A driveway needs a crushed-stone base under the decomposed granite. The base carries the vehicle load and keeps the DG from rutting. Compact the base before you spread any granite over it.

Edging holds the whole surface in place. Decomposed granite is loose material and it will creep sideways without a firm edge. Metal, stone, or a buried timber all work as a restraint. Set the edging to the finished height so it contains the top lift.

Install the edging before you spread the DG. Then fill against it, lift by lift, and compact each layer up to the edge. A firm perimeter stops the granite from spilling into beds and lawns. It keeps the crisp line that makes a DG path look finished.

Most DG shortfalls trace back to a few repeat errors. Knowing them ahead of time saves a second trip to the yard and a stalled job.

The first mistake is entering depth in the wrong units. The tool wants inches. If you type feet where inches belong, the estimate swings far off. Read your depth back before you trust the total. A 3 should mean 3 inches, not 3 feet.

The second mistake is forgetting compaction. Decomposed granite settles when it is packed. People order for the finished depth and come up short once the compactor runs. Order for the loose depth needed to reach the finished depth, or lean on the compaction allowance to cover it.

The third mistake is using one depth for every surface. A patio, a driveway, and a mulch bed each call for a different number. A driveway also needs a base under the DG. Match the depth to the job before you read the tonnage.

The fourth mistake is measuring a rough area as a clean rectangle. Curves, cutouts, and widened aprons change the true area. Break an odd shape into simple parts, size each part, then add them together. An area that is too small leaves you short of material.

The fifth mistake is ignoring the density range. Damp or very fine DG weighs more than the 1.4 planning value. If your supplier gives a plant-specific density, use theirs. A wrong density throws the ton count off even when the volume is right.

The last mistake is ordering exactly the estimate with no margin. Ground is uneven and spills happen. Keep the allowance on and round up to the next practical amount. A small surplus beats a second delivery.