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Decorative Stone & Garden Coverage

Landscape Rock Calculator

Calculate cubic yards and tons of river rock, decorative stone, and xeriscape ground cover. Includes stone-size depth rules to ensure complete ground coverage and prevent fabric exposure.

The "2× Diameter" Rule for Landscape Rock

When calculating coverage for decorative landscape rock, the most frequent mistake is applying standard 2-inch mulch depth to large stones. If you spread 2-to-3-inch river rocks only 2 inches deep, black landscape fabric will peek through between the stones, creating an unsightly checkerboard appearance.

Professional landscapers follow the "2× Diameter Rule":

  • Small Stones (1/2" to 1"): Minimum depth = 2 to 2.5 inches.
  • Medium River Rock (1" to 3"): Minimum depth = 3 to 4 inches.
  • Large Cobbles (3" to 5"): Minimum depth = 5 to 6 inches.
Landscape Rock Coverage Formula: 1. Bed Area (sq ft) = Length (ft) × Width (ft)
2. Depth in Feet = Depth based on stone size (inches) ÷ 12
3. Cubic Yards = [Area × Depth in Feet] ÷ 27
4. Recommended Yards = Cubic Yards × (1 + Ordering Adjustment % ÷ 100)
5. Tonnage (River Rock @ 1.22 tons/yd³) = Recommended Yards × 1.22

Worked Example: Perimeter Foundation Drip Edge

Project: 60 ft House Foundation Strip × 2 ft Wide with 1"–3" River Rock (10% Ordering Adjustment)
  1. Calculate Square Footage: 60 ft × 2 ft = 120 sq ft.
  2. Determine Depth for 1"–3" Rock: Following the 2× rock size guideline, use 3.5 inches (0.292 ft).
  3. Calculate Base Volume: 120 sq ft × 0.292 ft = 35.04 cubic feet.
  4. Convert to Cubic Yards: 35.04 cu ft ÷ 27 = 1.30 cubic yards.
  5. Apply 10% Ordering Adjustment: 1.30 yd³ × 1.10 = 1.43 recommended cubic yards (+0.13 yd³ allowance for subgrade variance and edge retention).
  6. Weight (Landscape Rock @ ~1.22 tons/yd³): 1.43 yd³ × 1.215 tons/yd³ ≈ 1.73 tons (3,465 lbs, or ~1.74 tons at 1.22 tons/yd³).

Benefits of Decorative Stone in Residential Landscaping

While landscape rock requires an initial investment, it offers permanent functional advantages:

  • House Foundation Splash Protection: A 2-foot strip of river rock beneath roof drip lines breaks rainfall impact, preventing mud from splashing against foundation siding and reducing soil erosion.
  • Wildfire & Heat Defense: Unlike dry pine bark or cedar mulch, landscape stone is completely non-combustible. Fire-wise landscaping guidelines in arid and western regions strongly recommend replacing organic mulch with stone within 5 feet of exterior building walls.
  • Rodent & Termite Deterrence: Wood mulch holds damp moisture and cellulose that attracts termites, carpenter ants, and burrowing rodents. Stone provides an inhospitable barrier around basement walls.

Frequently Asked Questions About Landscape Rock

The golden rule for landscape rock is that depth must be at least twice the diameter of the largest stone in the mix. For 1-inch stone, apply at 2 to 2.5 inches deep. For 1-to-3-inch river rock, apply at 3 to 4 inches deep. For larger 3-to-5-inch cobbles, a minimum depth of 5 to 6 inches is required to cover bare ground.

One cubic yard of washed 1-to-3-inch landscape river rock weighs approximately 2,430 pounds (about 1.22 US short tons). Because rounded rocks create large air gaps between individual stones, river rock is slightly lighter per cubic yard than dense crushed stone blends.

Landscape rock is a permanent, non-flammable ground cover that never decomposes, blows away in leaf blowers, or attracts termites. While its initial material and delivery cost is higher than mulch, it eliminates the recurring annual expense and labor of re-mulching.

Yes, absolutely. Without heavy commercial weed fabric beneath the stones, heavy river rocks will slowly sink into wet garden soil over 2 to 3 seasons, and stubborn weeds will root into the mud below.

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