Calculate Your Landscape Rock
Proper landscape rock depth prevents weeds and retains moisture. Standard: 2-3 inches over landscape fabric.
Landscape Rock Quantity Reference
A landscape rock calculator estimates cubic yards, tons, bags, and cost from bed area, depth, and rock type.
Common Rock Types
- River rock: rounded decorative rock, about 1.6 tons per cubic yard.
- Lava rock: lighter porous rock, about 1.25 tons per cubic yard.
- Mexican beach pebbles: premium decorative pebble, usually priced much higher.
- Flagstone: flat stone for paths and stepping areas.
- Boulders: large accent stones, often priced per piece.
Typical Depth
- Standard cover: 2 to 3 inches.
- Light decorative cover: 1 to 1.5 inches.
- Heavy weed suppression: about 4 inches.
Basic Formula
(Length x Width x Depth in inches) / 324 = Cubic yards
Example
A 20-foot by 8-foot bed at 2.5 inches deep equals about 1.23 cubic yards.
Fabric and Drainage Notes
- non-woven landscape fabric may reduce soil migration and weed growth
- rock used in drainage areas may need larger size and deeper placement
- decorative rock and mulch serve different visual and maintenance goals
Over time, landscape rocks sink into soil, especially in wet climates or poorly compacted soil. Prevention is easier than remediation.
Prevention Strategies
- Compact soil: Firmly tamp soil before laying fabric
- Use landscape fabric: Creates a barrier preventing sinking
- Proper depth: 2-3 inches allows settling without disappearing
- Edge containment: Use edging to keep rock contained
- Maintenance: Annually rake rock and refresh fabric
Remediation
If rocks have sunk significantly, partially remove the rock layer, replace or reinforce the landscape fabric, and redistribute the rock evenly.
Landscape Rock Reference Chart
| Rock Type | Tons/Cubic Yard | Recommended Depth | Cost/Ton | Best For |
|---|---|---|---|---|
| River Rock | 1.6 | 2-3 inches | $45-$65 | Decorative beds, water features |
| Lava Rock | 1.25 | 2-3 inches | $35-$55 | Dry climates, drainage |
| Mexican Pebbles | 1.55 | 2-3 inches | $55-$80 | Premium landscaping, patios |
| Flagstone | 1.8 | Varies | $60-$100 | Pathways, patios, edging |
| Large Boulders | 1.9 | Per piece | $200-$500+ per piece | Statement pieces, focal points |
Frequently Asked Questions
Use 2-3 inches of landscape rock. Two inches is the minimum for effective weed suppression. Three inches provides better coverage and appearance. Never exceed 4 inches unless you have severe weed issues or very heavy planting.
A cubic yard of landscape rock weighs 1.25-1.9 tons depending on type. River rock: 1.6 tons, lava rock: 1.25 tons, Mexican pebbles: 1.55 tons, flagstone: 1.8 tons, boulders: 1.9 tons.
Rock lasts longer and requires less maintenance but doesn't improve soil. Mulch improves soil but needs annual replacement. Rock is better for dry climates and permanent plantings. Mulch is better for humid climates and frequently-revised garden beds.
Firmly compact soil before installation, use landscape fabric underneath, maintain proper depth (2-3 inches), and use edging for containment. Annually rake rock and refresh fabric to prevent sinking.
River rock and lava rock both provide excellent drainage. Lava rock is superior due to its porous nature. Use these rocks in swales, around downspouts, and in low-lying areas prone to standing water.
