How This Calculator Works
Enter your area dimensions and rock depth, then select your rock type. The calculator computes volume in cubic feet, converts to cubic yards (divide by 27), and uses each rock's density to convert to tons. Lava rock is significantly lighter at 1,500 lbs per cubic yard compared to 2,800 lbs per cubic yard for boulders — meaning you need fewer tons of lava rock but the same volume.
Landscape Rock Types Compared
| Rock Type | Weight (lbs/yd³) | Cost per Ton | Sold By | Best For |
|---|---|---|---|---|
| Lava Rock | ~1,500 | $80-130 | Bag or bulk | Flower beds, fire pits, mulch alternative |
| Flagstone | ~2,600 | $100-200 | By the ton | Pathways, patios, stepping stones |
| River Rock | ~2,650 | $50-100 | Bag or bulk | Dry creek beds, borders, ground cover |
| Boulders | ~2,800 | $100-200 | By the ton | Accent features, retaining, focal points |
| Mexican Beach Pebbles | ~2,500 | $150-300 | Bag only | Premium ground cover, zen gardens, borders |
Coverage by Rock Size
Larger rocks leave more air gaps between stones, so they cover less area per ton than small stones. A ton of 1/2-inch pea gravel at 2 inches deep covers roughly 120 square feet. The same ton of 3-6 inch river rock at 2 inches deep covers only about 70-80 square feet because of the irregular spacing.
| Rock Size | 2" Depth (sq ft/ton) | 3" Depth (sq ft/ton) | 4" Depth (sq ft/ton) |
|---|---|---|---|
| Small (under 1") | ~120 | ~80 | ~60 |
| Medium (1-3") | ~100 | ~65 | ~50 |
| Large (3-6") | ~75 | ~50 | ~40 |
| Extra Large (6-12") | ~50 | ~35 | ~25 |
Cost Per Square Foot
At 2 inches deep, the cheapest option is bulk river rock at about $0.50-1.00 per square foot. Lava rock runs $0.75-1.50 per square foot despite being lighter because its unit cost is higher. Premium materials like Mexican Beach Pebbles can reach $3-5 per square foot. Buying in bulk (by the ton) saves 30-50% compared to bags from a home improvement store.
FAQ
How deep should landscape rock be?
For ground cover and weed prevention, 2-3 inches is standard. Garden beds and borders look best at 3-4 inches. If you are covering landscape fabric, 2 inches is the minimum to fully conceal the fabric and prevent UV degradation.
Does landscape rock attract bugs?
Rock generally attracts fewer pests than wood mulch because it does not decompose. However, moisture can collect under rocks and attract insects in humid climates. Installing landscape fabric underneath and ensuring proper drainage eliminates most pest issues.
How long does landscape rock last?
Indefinitely. Unlike mulch which breaks down every 1-2 years, rock does not decompose. Colors may fade slightly after 5-10 years with UV exposure, and some settling occurs, but you rarely need to replace landscape rock. That makes it cheaper long-term even though the upfront cost is higher.
Should I put landscape fabric under rocks?
For decorative areas, yes — woven landscape fabric prevents weeds while allowing water drainage. Avoid cheap plastic sheeting, which traps moisture and kills soil. In drainage areas or around plants where roots need to spread, skip the fabric entirely.
Related Calculators
- Gravel Calculator — for pea gravel, crushed stone, and driveway gravel
- Mulch Calculator — compare rock coverage vs mulch for your beds
- Retaining Wall Calculator — for landscape block walls and backfill
- Soil Volume Calculator — for garden beds and raised planters
Prices shown are approximate 2026 U.S. averages and may vary significantly by region, retailer, and market conditions. Always get local quotes for accurate pricing.