Should I put fabric under decorative stone?

Usually yes, and use woven landscape fabric rather than plastic sheet. Fabric lets water through and stops the stone working down into the soil, which is what makes a bed look thin after a couple of years. Plastic traps water and fails.

Is stone cheaper than mulch?

More expensive to buy and much cheaper over time, because it does not break down and need replacing every year or two. It also does not feed the soil, so it suits paths, borders and drainage rather than planting beds.

Why does my stone bed keep sinking?

Almost always because the stone is migrating into the soil below. Fabric underneath and a full depth of stone on top both fix it. Topping up on to an existing thin layer without fabric just repeats the problem.

Can I walk on river rock?

Not comfortably. Rounded stone shifts underfoot, which is why paths use angular crushed stone or decomposed granite instead: the pieces lock together. Keep rounded rock for beds and features you look at rather than walk on.

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Stone calculator: coverage, tonnage and boulder weight

This stone calculator covers decorative and landscape stone rather than base material: how far a ton goes at the depth you want, what a boulder weighs from its measurements, and how much flagstone an area takes.

Working out

Length (ft)

Width (ft)

Depth (in)

Stone type

How deep should decorative stone be?

Depth depends on the stone size, and getting it wrong is why some beds show weed fabric through the gaps and others sink underfoot.

Stone size	Depth	Use
Fine, under ½ in	1 - 2 in	Paths, ground cover
½ to 1 in	2 - 3 in	Beds, borders, drainage
1 to 2 in	3 - 4 in	Larger beds, dry creek beds
Over 2 in	4 in or more	Feature areas, erosion control

The rule of thumb: depth should be at least two to three times the stone diameter, or the individual pieces sit proud and shift when walked on.

How much does a ton of stone cover?

Roughly 120 square feet at 2 inches deep, or 80 square feet at 3 inches, for most decorative stone. Lighter materials such as lava rock cover almost twice as much, which is why it is often the cheapest option by area despite costing more by the ton.

Stone	Pounds per cubic yard	Per ton at 2 in	At 3 in
River rock	2,600	125 sq ft	83 sq ft
Marble chips	2,700	120 sq ft	80 sq ft
Slate chippings	2,600	125 sq ft	83 sq ft
Decomposed granite	2,900	112 sq ft	74 sq ft
Beach cobble	2,700	120 sq ft	80 sq ft
Lava rock	1,400	231 sq ft	154 sq ft

Figures derived from the densities in the second column, so they match what the calculator above returns. An earlier draft of this table used a general rule of thumb instead and was out by about a quarter.

Convention Densities are supplier averages and vary by source and moisture. No standards body governs decorative stone density, so ask for the weight per yard of the specific product before ordering a large quantity.

How do you work out what a boulder weighs?

Multiply the three dimensions to get a box, then take about 60 to 70% of it, because a boulder is not a cube. Multiply that volume by the rock density: granite is around 165 pounds per cubic foot, basalt nearer 170, limestone about 150.

The reason to work it out is access rather than curiosity. A boulder three feet by two by one and a half comes to roughly 965 pounds of granite, which is beyond a wheelbarrow and beyond two people. Anything over about 200 pounds needs machinery, and knowing that before delivery day saves an expensive surprise.

Common questions

Should I put fabric under decorative stone?: Usually yes, and use woven landscape fabric rather than plastic sheet. Fabric lets water through and stops the stone working down into the soil, which is what makes a bed look thin after a couple of years. Plastic traps water and fails.
Is stone cheaper than mulch?: More expensive to buy and much cheaper over time, because it does not break down and need replacing every year or two. It also does not feed the soil, so it suits paths, borders and drainage rather than planting beds.
Why does my stone bed keep sinking?: Almost always because the stone is migrating into the soil below. Fabric underneath and a full depth of stone on top both fix it. Topping up on to an existing thin layer without fabric just repeats the problem.
Can I walk on river rock?: Not comfortably. Rounded stone shifts underfoot, which is why paths use angular crushed stone or decomposed granite instead: the pieces lock together. Keep rounded rock for beds and features you look at rather than walk on.