Multiply length × width in feet by depth in feet, divide by 27 for cubic yards, then multiply by the rock density — 1.5 for river rock. A 25 × 8 ft bed at 2 inches deep needs about 1.23 cubic yards, or roughly 1.9 tons.
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Order – tons (includes your waste allowance) so compaction and spillage don’t leave you short.
Rock Calculator Guide
“Landscape rock” is a shelf label, not a material — behind it sit half a dozen products that differ in weight by a factor of two and in purpose by more than that. The estimating consequence is simple: you cannot price a rock project until you have picked the rock. This calculator carries the full lineup, from featherweight lava rock at 0.65 tons per cubic yard to riprap at 1.65, and converts your bed dimensions to tonnage for whichever you choose.
The default is river rock at 1.5 tons per cubic yard and a 2-inch depth — the most common combination in residential landscaping — but the interesting decisions happen when you deviate from it.
Which Landscape Rock Should You Choose?
Coverage figures below are per ton at a 2-inch layer; riprap is listed at its working 12-inch armor depth instead:
| Rock | Tons per yd³ | Coverage per ton | Reach for it when |
|---|---|---|---|
| Lava rock | 0.65 | 249 sq ft | Hauling by hand, hot dry beds |
| Pea gravel | 1.35 | 120 sq ft | Paths, play areas, patio joints |
| Marble chips | 1.35 | 120 sq ft | Bright formal accents |
| Decomposed granite | 1.40 | 116 sq ft | Firm natural-looking trails |
| Gravel | 1.40 | 116 sq ft | Utility cover, driveways |
| River rock | 1.50 | 108 sq ft | Dry creeks, drainage, ground cover |
| Riprap | 1.65 | 16 sq ft at 12 in | Slopes and shorelines under attack |
Reading the Table Like a Designer
Weight is a proxy for effort as much as cost. A ton of lava rock is fourteen wheelbarrow loads that feel like eight; a ton of river rock is ten loads that feel like fifteen. If your project is up a slope, through a gate, or behind the house, the light materials earn their premium in your shoulders. Conversely, weight is stability — light rock migrates in wind-scoured or high-runoff spots where river rock sits still for decades.
Mixing sizes is the professional move most DIY beds miss. A base of 3/4–1 inch stone with 10–15% larger accent rock scattered through it locks together better, hides fabric more completely, and reads more naturally than any single-size layer — and since the accents ride on top, they add looks without adding meaningful tonnage.
Once a specific material has won the argument, its dedicated tool sharpens the estimate — the river rock calculator for rounded stone and the decorative stone calculator for the show materials like marble chips and lava rock.
Frequently Asked Questions
How much rock do I need for 100 square feet?
At 2 inches deep, about 0.62 cubic yards — roughly 0.9 tons of river rock, or only about 0.4 tons if you choose lightweight lava rock. At 3 inches, add half again to either figure.
What size landscape rock should I pick?
Match size to job: 3/8-inch pea gravel for paths and between steppers, 3/4–1 inch rock for general ground cover, 1–3 inch for dry creeks and drainage, and 3-inch-plus accent stone where you want individual rocks to read from a distance.
Is rock better than mulch?
Rock never decomposes, never blows away, and never needs an annual top-up, but it holds summer heat and adds nothing to the soil. Most yards use both — rock near structures and paths, organic mulch in planting beds.
How deep should landscape rock be laid?
Roughly twice the diameter of the largest stone: 2 inches for rock up to an inch, 3–4 inches for 1–3 inch material. Shallower shows fabric through the gaps; deeper buys nothing but tonnage.