Decomposed Granite Calculator

Calculate decomposed granite by area and depth

The arithmetic is area times depth, converted to cubic yards, then increased for compaction. Measure the area in square feet, multiply by the depth in inches, divide by 12 to get cubic feet and by 27 to get cubic yards. That figure is the finished volume. Add 20% for loose DG or 25% for a stabilized mix and you have the loose volume to order.

At 3,000 lb per cubic yard, DG converts to tons by dividing by 2,000, so a cubic yard is 1.5 tons. Most yards sell it by the ton and quote by the ton, but stock it in cubic yard loader buckets, which is why the two units keep getting mixed up in the same conversation. The calculator prints both so you can order in whichever unit the supplier answers in.

For an irregular area, break it into rectangles and circles, work each one out, then add them together. Curved bed edges are close enough treated as rectangles at their average width. The compaction allowance absorbs that kind of rounding, which is one more reason not to skip it.

How deep should DG be?

Two inches for foot traffic, three for patios and seating, four or more where vehicles run. Those are compacted depths, so a 2 in path starts life as roughly 2.5 in of loose material before the plate compactor goes over it.

Read down the third column and the pattern is the one that catches people out: coverage halves as depth doubles. A ton spreads 108 sq ft at path depth but only 54 sq ft at driveway depth, so going one inch deeper across a large area costs a great deal more than it sounds like it should.

Deeper isn’t better. Past about four inches DG stops firming up properly through its full thickness and the top stays loose underfoot, because a plate compactor only influences the first few inches. If you need more build-up than that, put crushed base underneath and keep the DG layer to a surfacing thickness.

Stabilized vs loose DG, and why the quantities differ

Loose DG is screened granite fines with nothing added. Stabilized DG has a binder blended through it that sets as it dries and knits the fines together. Both are ordered the same way, but they do not compact the same amount, so the same finished path needs a different quantity depending on which you pick.

Stabilized and resin-coated mixes settle harder because the binder fills voids that would otherwise stay as air, so they take about 25% extra against 20% for loose. On a small path the difference is a wheelbarrow. On a 1,000 sq ft patio it is most of a ton, which is the sort of gap that turns into a second delivery charge.

The choice is really about maintenance rather than money. Loose DG is cheaper per ton and needs raking and topping up most years. Stabilized costs more up front and holds its surface through rain and traffic. Anywhere the path leads to a door, stabilized is worth it simply because loose fines walk indoors on shoes.

Coverage per ton, and what a cubic yard weighs

One ton of decomposed granite covers about 108 sq ft at 2 in, 72 sq ft at 3 in and 54 sq ft at 4 in, all compacted. A cubic yard weighs roughly 3,000 lb, which makes it 1.5 tons per cubic yard, or 0.67 cubic yards to the ton.

The third column is fixed arithmetic and worth memorising: a cubic yard of any material covers 324 sq ft at one inch, so divide 324 by your depth in inches and you have the coverage without touching a calculator. Weight per ton varies with density, but that yardage figure never does.

Quarry figures move around. Granite fines with more moisture in the pile can run 200 lb heavier per yard, and a drier screened product lighter. That’s a few percent on a small job and a real number on a truckload, so if your order sits near a weight limit, ask the yard what their material actually runs at.

DG for paths, patios and driveways

Each use wants a different depth and a different amount of preparation underneath, and the difference between them is mostly what happens below the DG rather than the DG itself.

Paths and walkways

Two inches over compacted subgrade, with edging both sides. Without edging the path spreads outward and thins in the middle within a year or two. A 3 ft wide path is the practical minimum for one person, 4 ft if two people walk abreast or a wheelbarrow has to pass.

Patios, seating and fire pit areas

Three inches, stabilized. Chair legs and table feet concentrate load onto a very small area and punch straight through a 2 in loose surface. Around a fire pit, extend the DG at least 3 ft past the pit edge so chairs sit on it rather than half on and half off. A 12 ft circle covers 113 sq ft, which at 3 in works out at 1.31 cubic yards of stabilized DG once compaction is allowed for, or almost two tons.

Driveways

Four inches of DG over 4 to 6 in of compacted crushed base. DG alone will rut under a car regardless of depth, because the load needs a graded stone layer beneath it to spread across. Stabilized is close to essential here, and even then expect to top up the wheel tracks periodically.

Ground cover between plantings

Two inches is plenty where nobody walks. DG suppresses weeds reasonably well and doesn’t blow around the way bark does, but it holds heat, so keep it clear of the crowns of anything that resents dry roots.

How much stabilizer you need

Budget roughly 36 lb of binder per cubic yard of DG, which works out at about 24 lb per ton. Rates differ between brands by a wide margin, so the number on your product data sheet beats any figure on a website including this one. The calculator has a field for it for exactly that reason.

Binder is blended dry through the DG before it goes down, not scattered over the top afterwards. A yard that sells stabilized DG will usually pre-blend it for a few dollars a ton, and that is money well spent because getting an even mix in a wheelbarrow is genuinely difficult. If you are mixing it yourself, do it on a tarp in small batches and turn it at least three times.

Once it is laid and levelled, water it in thoroughly, let it dry, then compact. The binder needs moisture to activate and time to cure, and walking on it early leaves prints that stay. Two or three days of dry weather after laying is the usual advice, and a job that gets rained on in the first day often has to be raked up and redone.

What decomposed granite costs

Loose DG runs about $40 to $70 a ton picked up, stabilized $70 to $120, and resin-coated more again. Delivery adds $75 to $150 within a normal radius, which is why a single larger order almost always beats two small ones. Prices vary sharply by region because DG is heavy and doesn’t travel economically, so a quarry an hour away can cost less delivered than one three hours away costs collected.

Installed, expect $4 to $8 a square foot for a stabilized path including excavation, base preparation, edging and compaction. Material is usually under a third of that figure. The labor sits in the preparation, and preparation is what decides whether the surface is still flat in five years.

Bagged DG is sold in half cubic foot bags at garden centers and works out at several times the bulk price per yard. It is the right call for patching a few square feet and the wrong call for anything larger. The rough crossover is around half a cubic yard, or about 27 bags, at which point a bulk delivery is cheaper even after the delivery fee.

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