How much rock mulch do I need?
Rock is the one ground cover that is almost always sold by weight, not by the bag, so this calculator works in tons. It first finds the volume — area times depth — converts it to cubic yards, then multiplies by the density of your stone to give a tonnage you can hand straight to the supplier. A 300-square-foot area at 2 inches deep is about 1.85 cubic yards, which at a typical 1.35 tons per cubic yard is roughly 2.5 tons. Adjust the density field to match your specific rock for a tighter estimate.
Why density matters
Two yards of pea gravel and two yards of river rock do not weigh the same, and that difference shows up on your invoice. Most landscape rock and gravel falls between about 1.3 and 1.6 tons per cubic yard, but dense or wet stone runs heavier. If your supplier publishes a weight per cubic yard, enter it; if not, 1.35 is a reasonable middle-of-the-road default. Get the density roughly right and your tonnage — and therefore your cost — will be close. This is the single biggest source of error in rock estimates, which is why we put the density front and center.
How deep should rock go?
For most decorative applications, 2–3 inches of rock gives full coverage that hides the ground beneath without burying your edging. Smaller stones can go a touch shallower; larger cobble needs a bit more depth to look intentional and stay put. Unlike wood mulch, rock does not decompose, so you are buying the full depth once. Lay landscape fabric underneath to block weeds and to keep the stone from sinking into the soil over time.
Rock vs. organic mulch
Rock mulch wins on permanence: it never needs replacing, it will not blow away, and it is excellent for drainage strips, dry creek beds, fire-wise zones and high-wind spots. The trade-offs are real, though — it adds no nutrients to the soil, it reflects heat onto nearby plants, and it is genuinely hard to remove if you change your mind. For planting beds you intend to amend, organic bark mulch is usually the better long-term choice. For pathways, borders and low-maintenance ground cover, rock is tough to beat.
Ordering with confidence
Because rock is heavy and usually delivered loose, ordering the right amount the first time matters even more than with bagged products. Break your project into separate areas, add a bed for each, and keep a small waste margin for uneven spreading and settling. When the tonnage looks right, copy or print the estimate — handing your supplier a clear figure in tons and cubic yards is the fastest way to an accurate quote and a single, correctly sized delivery.