How Deep Should Gravel Be

TL;DR

Most gravel work lands between 2 and 6 inches of stone. A garden path or a decorative bed can stop at 2 or 3 inches. A driveway needs a packed layer of Road Base under its surface stone, so the two layers together reach 6 inches or more. A patio base and a drain trench go deeper again, because one carries weight and the other carries water.^[1]

To order, change the depth from inches to feet, multiply by the area, and divide by 27 to get cubic yards. The weight of one cubic yard of your material then gives tons. As a yardstick, 100 square feet of #57 Crushed Stone at 4 inches deep comes to 1.67 tons.^[1],[2]

Key Takeaways

Choose depth by what the surface must carry, because feet need far less stone than tires do.^[1]

Build a driveway in two layers, a compacted Road Base below and a thin clean stone such as Driveway Gravel on top.^[1]

Keep rounded Pea Gravel near 2 or 3 inches deep so it stays put underfoot.^[1]

Make a stone bed at least as deep as its largest stones, so River Rock at 1 to 3 inches wants close to 3 inches of cover.^[1]

Divide inches by 12 before you multiply by area, or your cubic feet will come out far too high.^[2]

Expect a heavy material to need more tons for the same depth, since Road Base at 2,800 lb per cubic yard outweighs Decomposed Granite at 2,500 lb.^[1]

Measure a base after it is packed, and order a modest margin of extra Road Base to cover the loss in volume.^[1]

How deep a gravel driveway should be

A gravel driveway works best as a two layer build. The lower layer is Road Base, a 3/4 inch minus blend whose fines fill the gaps between its angular pieces. It is spread, dampened and rolled or tamped until a boot heel barely marks it. The upper layer is a clean stone such as Driveway Gravel, which is 3/4 inch clean crushed, so tires get grip and rain drains through. For a home drive, plan on 4 to 6 inches of Road Base and 2 to 3 inches of surface stone.^[1]

Soft or wet ground calls for the thick end of that range. Clay that stays damp after rain, or a drive that sees a heavy pickup or a camper, gains from the full 6 inches of base. Spread that base in two passes and pack each one, so the bottom of the layer gets as firm as the top. Firm, well drained ground can get by with 4 inches. Keep the surface stone thin no matter what sits below it. A deep pile of clean stone on top behaves like loose fill, and wheels dig ruts into it instead of rolling across.^[1]

On 100 square feet of drive, 4 inches of Road Base takes 1.73 tons and 6 inches takes 2.59 tons. A 2 inch top of Driveway Gravel over that same patch adds 0.83 tons, and a 3 inch top adds 1.25 tons. A drive with twice that area needs twice each of those amounts.^[1]

#57 Crushed Stone, sized 3/4 to 1 inch, also makes a good surface stone. It weighs 2,700 lb per cubic yard, the same as Driveway Gravel, so a top layer of either one comes to the same tonnage at the same depth.^[1]

How deep a garden path should be

A path carries people, a wheelbarrow and the odd garden cart, so it needs far less stone than a drive. A layer of 2 to 3 inches hides the soil and gives a clean, even walking surface. Going deeper only makes the stone shift and roll when you step on it.^[1]

Pea Gravel and Walkway Gravel are both 3/8 inch, a size that feels comfortable under a shoe. Pea Gravel is round, so it moves more than an angular stone. Hold it near 2 inches on a path that sees daily foot traffic, and use 3 inches where you want a fuller look. For 100 square feet, 2 inches of Pea Gravel takes 0.80 tons and 3 inches takes 1.20 tons. Walkway Gravel shares the same weight of 2,600 lb per cubic yard, so its tonnage matches at each depth.^[1]

Decomposed Granite builds a firmer path, because its 1/4 inch and fines texture packs into a surface close to hard. Lay about 3 inches, mist it with a hose, and tamp it in thin passes until it stops moving. At that depth, 100 square feet takes 1.16 tons. Its gold to tan color suits a garden that wants a warmer look than gray stone.^[1]

Edging matters as much as depth on any path. Without a steel, stone or timber border, the stone drifts into the lawn and the layer thins out at its sides. Where a path will carry loaded wheelbarrows, a 2 inch layer of Road Base under the surface stone keeps tire tracks from cutting through, and it adds 0.86 tons per 100 square feet.^[1]

How deep the base under a patio or pavers should be

Pavers and flagstone rest on a packed base of Road Base with a thin setting bed on top. For a patio that carries chairs, a grill and people, the base is 4 inches deep once packed. For a paver walk or parking pad that will see a car, go to 6 inches. Dig out enough soil for the base, the bed and the thickness of the pavers, so the finished surface sits where you want it.^[1]

The setting bed is Stone Dust Screenings, 1/4 inch and fines, spread about 1 inch thick and pulled flat with a straight board. The pavers bed into it and lock in place. A thicker bed can sag under traffic and leave pavers out of line. For 100 square feet, a 2 inch layer of Stone Dust Screenings takes 0.86 tons, so a 1 inch bed needs about half of that.^[1]

A patio needs more depth than a path because the load is concentrated. A table leg or a car tire presses on a small spot, and a thin base lets that spot sink. Where the ground freezes hard in winter, a deeper base can also keep the surface flatter as the soil swells and settles. Let the base run a few inches past the edge of the pavers, so the outer row has support under it.^[1]

For the base itself, 100 square feet at 4 inches takes 1.73 tons of Road Base, and at 6 inches it takes 2.59 tons. Road Base and Stone Dust Screenings both weigh 2,800 lb per cubic yard, which makes them the heaviest materials in this guide for a given depth.^[1]

How deep a drain rock trench should be

A drain trench is set by the depth you dig, so its stone fills the whole trench rather than sitting as a thin layer. Drain Rock, 3/4 to 1-1/2 inches, is the stone for the job. Its pieces are washed and sized alike, so the gaps between them stay open and water moves through them quickly. Most yard trenches run somewhere between one and two feet deep.^[1]

Line the trench with filter fabric first, so soil cannot wash into the stone and clog it over the years. If the trench holds a perforated pipe, lay at least 2 inches of Drain Rock on the trench floor before the pipe goes in, so water can reach it from below. Cover the pipe with more stone, fold the fabric over the top, and finish with soil, sod or a band of decorative stone.^[1]

The same math works for a trench as for a patio. Multiply the trench length by its width to get the floor area, then use the depth. For every 100 square feet of trench floor, each 6 inches of Drain Rock takes 2.50 tons. A trench a foot deep holds twice that, since a foot is 12 inches.^[1],[2]

Avoid swapping in a stone that carries fines. Road Base and Stone Dust Screenings pack tight, which is the right trait under a patio and the wrong one in a drain. In a trench, they slow water down instead of carrying it away.^[1]

How thick a decorative stone bed should be

A stone bed only has to cover the ground and stop light from reaching weed seeds, so depth follows stone size. Make the layer at least as deep as the largest stones in it. River Rock runs 1 to 3 inches, so a bed of it needs close to 3 inches, or bare fabric and soil peek out between the stones.^[1]

For 100 square feet, River Rock at 2 inches takes 0.80 tons and at 3 inches takes 1.20 tons. Its mixed earth tones blend with planting and with wood or brick trim. Pea Gravel, at 3/8 inch, can cover a bed at 2 inches because its small stones knit into a full layer sooner. Its mixed tan and brown color gives a softer look than gray stone.^[1]

#57 Crushed Stone gives a crisp, gray finish that suits a modern yard or a strip beside a foundation. At 3 inches it covers fabric well, and 100 square feet takes 1.25 tons. Angular stone also stays on a gentle slope better than round stone does.^[1]

Extra depth brings little gain in a bed. More stone means more weight to haul in, more work when you add a plant later, and no better weed control once the ground is covered. Lay fabric under the stone, keep the layer near the stone size, and top it up in later seasons where it thins.^[1]

How to turn depth into cubic yards and tons

Four steps turn any depth into an order. First, change inches to feet by dividing by 12, since there are 12 inches in a foot. Second, multiply the area in square feet by that depth in feet to get cubic feet. Third, divide by 27, the number of cubic feet in one cubic yard. Fourth, multiply the cubic yards by the weight of one cubic yard of your material, then divide the pounds by 2,000 to get tons.^[2]

The weight in that last step changes the answer from one material to the next. Road Base and Stone Dust Screenings weigh 2,800 lb per cubic yard. #57 Crushed Stone, Driveway Gravel and Drain Rock weigh 2,700 lb. Pea Gravel, Walkway Gravel and River Rock weigh 2,600 lb, and Decomposed Granite weighs 2,500 lb.^[1]

That spread shows up in real orders. The same 4 inches over 100 square feet is 1.73 tons of Road Base but 1.54 tons of Decomposed Granite. Order by the weight of the material you will spread, not by a figure you read for a different stone.^[1]

Area and depth both scale in a straight line. Double the depth and you double the stone, which you can see in #57 Crushed Stone at 0.83 tons for 2 inches and 1.67 tons for 4 inches on 100 square feet. Double the area and the tonnage doubles too. For an odd shaped yard, split it into rectangles, work each one out, and add them up.^[1]

Why packing and settling change the depth you order

Every depth in this guide means the layer as it ends up in place. Materials with fines lose volume when they are packed. Road Base and Stone Dust Screenings settle as their fine particles slide into the gaps, so a loose layer you spread will end up thinner once a plate compactor or roller goes over it.^[1]

Clean stone settles far less. #57 Crushed Stone, Drain Rock and Driveway Gravel have no fines to fill their gaps, so they shift a little as they seat and then hold their depth. Pea Gravel barely packs at all, which is why it never forms a firm surface on its own.^[1]

Plan for that loss in a base. Order a modest margin of Road Base above the packed depth you need, and spread it in passes no thicker than a compactor can push through. Check the depth with a stake and a string line after each pass as well as at the end, and fill low spots before the next layer goes down.^[1]

Ground that is uneven before you start throws off every figure. A yard that dips in the middle will swallow more stone there than the math predicts. Rake the soil smooth, pack it, and remove sod and roots first, so the stone you order goes into the layer you designed instead of into holes below it.^[1]