Stone Mulch Calculator
Calculate decorative stone mulch in tons and cubic yards. Supports river rock and crushed stone presets.
Stone Mulch Calculator
River rock, crushed stone, and pea gravel in tons
What Are the Main Stone Mulch Types?
Stone mulch comes in four main types: river rock, crushed stone, decorative stone, and pea gravel. River rock is smooth and rounded, sized 1 to 3 inches, and used for beds and drainage. Crushed stone is angular and sized 3/8 to 1 inch, used for paths and driveways. Decorative stone covers colored options like lava rock and marble chips for accent beds. Pea gravel is small rounded stone, 3/8 inch wide, used for walkways and patio bases. The Mulch and Soil Council (MSC) classifies all stone as inorganic mulch. Inorganic mulch does not break down, so it lasts a permanent 20 plus years. River rock is the top choice for French drains because water flows freely through the rounded gaps.
How Many Tons Per Yard Does Stone Weigh?
Stone weighs 1.4 to 1.75 tons per cubic yard. River rock weighs 2900 lbs per yard, which equals 1.45 tons. Crushed stone weighs 2800 lbs per yard, or 1.4 tons. Pea gravel also weighs 2800 lbs per yard. The formula is Length x Width x Depth / 27 = cubic yards. Multiply cubic yards by the weight factor to get tons. A 20 x 10 ft bed at 3 inches deep needs 1.85 cubic yards and 2.69 tons of river rock. Suppliers sell stone by the ton for delivery and by the yard for volume, so both numbers matter when ordering.
| Stone Type | Lbs per Yard | Tons per Yard |
|---|---|---|
| River rock | 2,900 lbs | 1.40 to 1.75 tons |
| Crushed stone | 2,800 lbs | 1.40 to 1.70 tons |
| Pea gravel | 2,800 lbs | 1.40 tons |
| Decorative stone | 2,800 to 2,900 lbs | 1.40 to 1.45 tons |
What Is the Correct Coverage Depth for Stone?
Apply decorative stone 2 to 3 inches deep and drainage stone 3 to 4 inches deep. One ton of stone covers 240 sq ft at 1 inch, 120 sq ft at 2 inches, 80 sq ft at 3 inches, and 60 sq ft at 4 inches. Decorative beds use 2 to 3 inches for full color coverage. French drains and downspout areas use 3 to 4 inches so water moves fast. Pea gravel works at 2 inches for walkways. River rock needs 3 inches minimum to hide the landscape fabric below. Stone retains heat in summer, so keep it away from heat-sensitive plant roots.
| Depth | Coverage per Ton | Best Use |
|---|---|---|
| 1 inch | 240 sq ft | Light top-dress |
| 2 inches | 120 sq ft | Decorative beds |
| 3 inches | 80 sq ft | Standard beds, paths |
| 4 inches | 60 sq ft | Drainage, French drains |
Why does river rock not compact?
River rock does not compact because the smooth rounded stones roll and shift under pressure. The rounded shape leaves open gaps, so water drains through freely. This makes river rock the standard fill for French drains. Crushed stone compacts and locks tight because the angular faces grip each other. Use crushed stone for paths that need a firm surface and river rock for drainage and decorative beds.
Why is landscape fabric mandatory under stone?
Landscape fabric is mandatory under stone mulch for three reasons. First, fabric stops the stone sinking into soft soil over time. Second, fabric blocks weeds from pushing up through the stone layer. Third, fabric keeps the stone clean and easy to rake. The National Association of Landscape Professionals (NALP) requires fabric underneath every stone install. Skipping fabric mixes stone with mud within two seasons.
How does stone mulch compare to wood mulch?
Stone mulch lasts 20 plus years while wood mulch lasts 1 to 4 years. Stone is inorganic and never breaks down, so it never feeds the soil. Wood mulch is organic and improves soil as it decomposes. Stone costs more upfront but needs no annual refresh. Stone retains heat, which suits desert plants but stresses moisture-loving plants. Choose stone for permanent low-maintenance areas and wood for plant beds.
FAQ
A 200 sq ft bed at 3 inches deep needs 2.5 tons of river rock or 1.85 cubic yards. At 2 inches deep it needs 1.7 tons. Order 2.75 tons to cover the 10 percent buffer. One ton covers 80 sq ft at 3 inches.
Multiply cubic yards by the stone weight factor. River rock uses 1.45 tons per yard. Crushed stone and pea gravel use 1.4 tons per yard. A 3 yard order of river rock equals 4.35 tons. Suppliers price delivery by the ton, so this conversion sets your cost.
River rock is better for drainage because the rounded stones leave open gaps for water. River rock is the standard fill for French drains. Crushed stone packs tight and slows water flow. Use crushed stone where you want a firm walking surface instead.
Stone mulch lasts a permanent 20 plus years because it is inorganic and does not break down. The Mulch and Soil Council (MSC) classifies stone as inorganic mulch. You rake it level every few years but never replace it. Wood mulch needs replacing every 1 to 4 years by contrast.
Stone mulch retains heat and raises soil temperature in summer. Stone absorbs sun all day and radiates heat into the bed. This suits cactus, succulents, and desert plants. Keep stone away from shallow-rooted shade plants. Apply 2 to 3 inches over landscape fabric to limit heat transfer.
One ton of stone covers 120 sq ft at 2 inches deep. At 1 inch it covers 240 sq ft, at 3 inches it covers 80 sq ft, and at 4 inches it covers 60 sq ft. Use the 2 inch depth for decorative beds and 3 to 4 inches for drainage.
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