Multiply area in square feet by depth in feet and divide by 27 for cubic yards, then multiply by the rock’s density. A 15 × 10 ft area under 2 inches of river rock needs about 0.9 cubic yards, or roughly 1.4 tons — the same area in lightweight lava rock weighs only 0.6 tons.
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Order – tons (includes your waste allowance) so compaction and spillage don’t leave you short.
Landscape Rock Calculator Guide
Two beds of identical size can need wildly different tonnage depending on what fills them: a yard of lava rock weighs 0.65 tons while a yard of river rock weighs 1.5 — more than double. That is why this calculator asks for the rock type before it quotes tons. Pick the material, enter the area and depth, and the density conversion produces a number your supplier can load straight onto the scale.
The choice of rock is really three decisions in one: the look you want, the maintenance you will tolerate, and the price per covered square foot — which depends on density as much as on the per-ton price tag.
Which Landscape Rock Should You Choose?
| Rock | Tons per yd³ | 1 ton covers at 2 in | Character |
|---|---|---|---|
| River rock | 1.50 | 108 sq ft | Smooth, rounded, natural mixed color; heavy enough to stay put |
| Pea gravel | 1.35 | 120 sq ft | Small, soft underfoot, budget-friendly; migrates without edging |
| Lava rock | 0.65 | 249 sq ft | Porous red or black; featherweight to spread, can crunch and drift |
| Marble chips | 1.35 | 120 sq ft | Bright white and formal; reflects heat, slowly raises soil pH |
| Decomposed granite | 1.40 | 116 sq ft | Compacts into a firm rustic surface; dusty when bone dry |
Coverage per ton is where light rock earns its keep: lava rock covers well over twice the area of river rock per ton, which often cancels out a higher sticker price. Heavy rock earns its keep in permanence — it resists wind, leaf blowers, downpours, and dogs.
Maintenance and Ordering Advice
Match the rock to the duty. In beds under trees, choose a mixed-color rock that hides leaf litter and stands up to blowing — river rock is the easy winner. In hot, bright exposures, skip white marble unless you want reflected glare on the siding. Anywhere a hose, mower, or foot traffic crosses the bed, avoid lava rock, which fragments underfoot and floats in heavy rain.
Order all of one material at once, from one supplier: color and size grading vary batch to batch, and a top-up from a different pit rarely blends invisibly. Keep 5–10% of the delivery in reserve buckets for future patching. Decorative layers also thin over the years as stone works into the soil, so plan on refreshing roughly an inch every three to five years — fabric underneath stretches that interval considerably.
For a deeper dive into the two most popular choices, see the dedicated river rock calculator and pea gravel calculator, which cover sizing, edging, and per-material project math.
Frequently Asked Questions
Which landscape rock covers the most area per ton?
Lava rock, by a wide margin — at just 0.65 tons per cubic yard, one ton spreads over roughly 249 square feet at 2 inches deep. River rock is the heaviest common choice at 1.5 tons per cubic yard, so a ton covers only about 108 square feet.
What is the lowest-maintenance landscape rock?
River rock 1.5 inches and larger stays put in wind, rain, and leaf-blowing, and its mixed natural color hides debris. Pea gravel and lava rock migrate more easily and usually need solid edging plus occasional raking back into place.
Do marble chips affect soil or plants?
White marble chips slowly leach calcium carbonate, which nudges soil pH upward — fine near most shrubs, but a poor match for acid-loving plants like azaleas and blueberries. They also reflect heat and glare in full sun.
Should I choose pea gravel or river rock?
Pea gravel is smaller, cheaper, and comfortable underfoot, which suits paths and seating areas, but it scatters without edging. River rock is larger and heavier, so it holds position in beds and drainage swales where pea gravel would wash.