How to calculate landscape rock
Tons = Cubic yards × lb per yd³ ÷ 2,000
Example: a 3 ft × 30 ft border of river rock at 3 inches deep is 90 × 3 ÷ 12 = 22.5 cubic feet = 0.83 cubic yards — about 1.1 tons.
How deep should decorative rock be?
A common rule of thumb is a layer about twice as deep as the stones are wide, so no soil or fabric shows through:
| Rock size | Typical depth |
|---|---|
| Small (⅜–¾ in): chips, small river rock | 2 in |
| Medium (1–2 in) | 3 in |
| Large (2–4 in) river rock | 4–5 in |
| Decomposed granite path (compacted) | 3 in |
Why lava rock is different
Lava rock is porous and very light — a cubic yard weighs less than half as much as river rock. If your supplier sells it by the ton, you will get a lot more volume per ton.
Frequently asked questions
How much does a yard of river rock weigh?
About 2,600 lb (1.3 tons), depending on size and moisture.
How much area does a ton of river rock cover?
About 120 sq ft at 2 inches, or 80 sq ft at 3 inches.
Do I need landscape fabric under rock?
It is recommended in beds to slow weeds and stop the rock sinking into the soil.
How much does a yard of lava rock weigh?
Often around 1,000 lb, but it varies a lot by source — check with your supplier.
Related calculators
These figures are estimates for planning only. Material weights and coverage vary by supplier, moisture and compaction. Always confirm quantities and prices with your supplier before ordering. See our terms & disclaimer.