Landscape Rock Calculator
Calculate tons of landscape rock, river rock, or gravel needed by coverage area and depth. Enter values for instant results with step-by-step formulas.
Reviewed by Abdullah, Technical Content Specialist
Formula
Tons = (Length x Width x Depth/12) / 27 x Weight per Cubic Yard / 2000
Where Length and Width are in feet, Depth is in inches (divided by 12 for feet), 27 converts cubic feet to cubic yards, Weight per Cubic Yard depends on rock type (1,500 to 2,900 lbs), and 2,000 converts pounds to tons. Different rock types have different densities, significantly affecting the tonnage needed for the same volume.
Worked Examples
Example 1: Decorative River Rock Border
Problem:A homeowner wants to install river rock around a 30 ft x 4 ft garden border at 3 inches deep. River rock costs $55/ton. Calculate materials needed.
Solution:Area = 30 x 4 = 120 sq ft\nDepth = 3 inches = 0.25 ft\nVolume = 120 x 0.25 = 30 cubic feet = 1.11 cubic yards\nRiver rock weight = 2,700 lbs/cu yd\nTotal weight = 1.11 x 2,700 = 2,997 lbs = 1.50 tons\nMaterial cost = 1.50 x $55 = $82.50\nDelivery = $85\nTotal = $167.50\nFabric needed: 120 x 1.15 = 138 sq ft (1 roll)
Result:1.11 cu yd | 1.50 tons | $167.50 total | 1 fabric roll needed
Example 2: Lava Rock Garden Coverage
Problem:Fill a 20 ft x 15 ft area with 4 inches of lava rock at $65/ton. Compare weight to equivalent gravel coverage.
Solution:Area = 20 x 15 = 300 sq ft\nDepth = 4 inches = 0.333 ft\nVolume = 300 x 0.333 = 100 cubic feet = 3.70 cubic yards\nLava rock: 3.70 x 1,500 = 5,556 lbs = 2.78 tons\nEquivalent gravel: 3.70 x 2,800 = 10,370 lbs = 5.19 tons\nLava rock cost: 2.78 x $65 = $180.56 + $85 delivery = $265.56\nWeight savings vs gravel: 5.19 - 2.78 = 2.41 tons lighter
Result:Lava: 2.78 tons ($266) | Equivalent gravel: 5.19 tons | 46% lighter with lava rock
Frequently Asked Questions
How do I calculate how many tons of landscape rock I need?
Calculating landscape rock tonnage requires knowing three things: the area to cover (length times width in feet), the desired depth in inches, and the weight of your chosen rock type per cubic yard. First calculate cubic yards by multiplying length times width times depth in inches, dividing by 12 to convert inches to feet, then dividing by 27 to convert cubic feet to cubic yards. Then multiply cubic yards by the rock weight per cubic yard and divide by 2,000 to convert pounds to tons. For example, covering a 15x10 foot area with 3 inches of pea gravel: 15 x 10 x (3/12) = 37.5 cubic feet = 1.39 cubic yards. At 2,800 lbs/yard, that is 3,889 lbs or 1.94 tons. Always round up and add 5 to 10 percent extra for edges and settling.
What are the most popular types of landscape rock and their uses?
Pea gravel (3/8 inch diameter, rounded) is popular for pathways, patios, and garden borders due to its smooth texture and drainage properties. River rock (1 to 3 inches, smooth) is ideal for dry creek beds, borders, and decorative accents. Crushed stone (angular, various sizes) works best for driveways, drainage, and compactable base layers. Decomposed granite (fine, sandy texture) creates natural-looking pathways and serves as ground cover in xeriscaping. Lava rock (lightweight, porous) excels in low-maintenance gardens and around fire pits due to heat resistance. Marble chips (white, elegant) provide bright contrast in formal landscapes. Slate chips (flat, dark) create a modern aesthetic for walkways. Each type has different weights per cubic yard, affecting how much you need to order by tonnage.
How deep should landscape rock be installed?
Depth depends on rock size and application. Small decorative rocks like pea gravel and marble chips should be 2 to 3 inches deep for adequate coverage while maintaining a natural appearance. Medium rocks (1 to 3 inch river rock) need 3 to 4 inches to provide complete coverage and prevent the landscape fabric beneath from showing through. Large decorative boulders and cobbles may only need a single layer placed strategically. For functional applications, driveway base rock should be 4 to 6 inches of compacted crushed stone, drainage rock around foundations needs 4 to 6 inches, and French drain rock requires 6 to 12 inches. Pathways generally need 2 to 3 inches of decorative rock over 4 inches of compacted base. Installing rock too thin results in visible fabric, weed penetration, and displacement, while too thick wastes material and money.
Why does landscape rock weight vary by type?
Landscape rock weight per cubic yard varies dramatically based on mineral composition, density, porosity, and moisture content. Dense igneous rocks like basalt and granite weigh 2,700 to 2,900 pounds per cubic yard because their crystalline structure contains tightly packed minerals. Sedimentary rocks like limestone and sandstone are slightly lighter at 2,500 to 2,700 pounds due to their layered, sometimes porous structure. Lava rock is exceptionally lightweight at only 1,400 to 1,600 pounds per cubic yard because it is filled with air pockets (vesicles) created by trapped gas bubbles during volcanic cooling. Shape also matters: angular crushed stone packs more densely than rounded river rock of the same material, adding 5 to 10 percent more weight per cubic yard. Moisture content can add 10 to 15 percent additional weight to dry weights.
References
Reviewed by Abdullah, Technical Content Specialist · Editorial policy