Landscape Rock Calculator

How landscape rock is estimated

Measure each bed, work out its square feet, multiply by the depth and convert to cubic yards. Then use the weight of the rock you want to convert yards to tons, because yards sell some rock and tons sell the rest. A 20 × 5 ft bed at 3 in is 25 cubic feet, or 0.93 cubic yards; with a 5% allowance, 0.97. In river rock at 1.35 tons a yard that is 1.31 tons, or 53 bags of 0.5 cubic feet. In lava rock at 0.68 tons a yard it is 0.66 tons.

Curved beds are easier to measure as a rectangle and a circle, or as a known area from a plan or a measuring app. Use up to three beds on this page and it adds them.

How deep to lay it

Extension guides do not fully agree, and it is worth knowing why. Utah State University Extension says 2 to 3 inches of inorganic mulch and names gravel, crushed stone, lava rock and cobbles. University of Nevada Extension says landscape fabric under a two inch layer of rock is sufficient. Colorado State University Extension says 4 inches of mulch needs no fabric underneath, and that stones larger than about half an inch do not work as mulch and can inhibit plants.

In practice that means 2 to 3 in over a breathable fabric for most beds, or about 4 in of small stone with no fabric. Colorado State warns against woven plastic fabric beneath mulch in landscape beds, while Nevada recommends fabric under rock in desert landscapes, so follow your local extension office. Large cobbles in a dry creek are decoration rather than mulch and go as deep as the stones need. Rock also holds heat: Nevada calls rock mulches hot and heavy, and Colorado notes gravel transfers more heat into the soil than wood chips, so keep it clear of plants that dislike it.

Weight and coverage by rock type

The page's starting weights and what a ton covers at two depths. These are typical values rather than a standard: rock varies with the stone, its size and how wet it is, so type your supplier's figure into the calculator when you have one.

Bags or bulk

Bagged rock usually comes as 0.5 cubic feet, so a cubic yard is 54 bags. Enter the bag price and the yard's price per cubic yard or ton in turn, add the delivery fee, and compare the delivered cost. Bags make sense for a small bed or a place a truck cannot reach; a load of bulk rock usually wins once the job runs to a yard or more, but check your yard's minimum and delivery fee.

Lava rock is often priced by the yard and river rock by the ton. A low price per ton of heavy rock can cost more than it looks, and the page converts between them using the weight above, so change that weight when your supplier gives you one.

How this differs from the gravel calculator

The gravel calculator is the general estimate for a driveway, a path or a base, with sand, topsoil and mulch as well. This page uses the same maths for decorative rock in a bed: it lists landscape rock types with their own weights, including lava rock at about half the weight of river rock, it starts at bed depth rather than base depth, it tells you when your depth falls outside what the extension guides name, and it adds a delivery fee and how far a ton goes. For a driveway or a compacted base, use the gravel calculator.

For landscaping contractors and supply reps: what to write down

On the walk-through, note each bed's size, the rock the client has in mind and its size and color, the depth you agreed, whether old rock or mulch comes out first, the fabric, the edging, where the truck can tip and how far it has to be barrowed. Read the yards and the delivered price back to the client before you leave, so the quote matches what you both saw.

Sources, each read on 2026-11-02. The weights come from bag labels and one landscape yard, so treat them as typical, not exact:

• Utah State University Extension, Water-Wise Landscaping: Mulch: inorganic mulch 2 to 3 inches; gravel, crushed stone, lava rock, cobbles
• University of Nevada Extension, Mulches for Nevada Landscapes (SP 06-10): fabric under a two inch layer of rock; decomposed granite listed as a mulch
• Colorado State University Extension, Mulching (CMG GardenNotes #245): 4 inches without fabric, stones under about half an inch, heat
• Earth Stone & Rock (California and Arizona landscape yard), Cubic Yards vs. Tons: river rock about 2,900 lb a yard, pea gravel and decomposed granite about 2,700, landscape rock about 2,800
• Vigoro River Pebbles, reseller listing: 50 lb per 0.5 cu ft bag
• Greensmix Red Volcanic Rock, retailer listing: 25 lb per 0.5 cu ft bag
• Pavestone Red Volcanic Rock, retailer listing: 19 lb per 0.5 cu ft bag
• Engineering ToolBox, Dirt and Mud Densities: dry gravel 105 lb per cubic foot

Related: the gravel calculator for driveways, paths and bases, the mulch calculator if you are comparing rock with bark, and the paver calculator for a patio next to the bed.

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• Mulch CalculatorWork out how many cubic yards or bags of mulch your beds need from their size and depth, with coverage per yard and the cost.Open the tool
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