Methodology
How we calculate river rock quantities and costs — the exact formulas, the density values behind every result, our data sources, and how we keep them current.
Last updated: 2026-06-10
We built this site to give homeowners and contractors a quantity and cost estimate they can actually trust. That means being transparent about how the numbers are produced. This page documents the formulas the calculator uses, the densities behind weight and coverage figures, the assumptions we make, and where our data comes from. Nothing here is hidden inside the tool.
The formulas we use
Every result starts from the same volume calculation, then converts into the units suppliers sell in:
Cubic feet = Area (ft²) × (Depth in inches ÷ 12) × (1 + waste) Cubic yards = Cubic feet ÷ 27 Tons = Cubic feet × density (lb/ft³) ÷ 2,000 Bags = Cubic feet ÷ bag size (ft³), rounded up
Area is calculated per shape — rectangles (length × width), circles (π × radius²), rings (π × [outer radius² − inner radius²]), triangles, and trapezoids — and multiple areas are summed. Bags are always rounded up to the next whole bag, because you can't buy a partial bag and rounding down leaves you short. The full step-by-step is on our how to calculate river rock guide.
The overage (waste) allowance
We default to a 10% overage, which you can adjust from 0–20% in the calculator. Some stone is always lost to uneven ground, settling, and spillage, and running short mid-project is far more costly than a small surplus. Ten percent is a practical, widely used allowance for loose decorative stone; deeper or more irregular projects (like dry creek beds) may warrant slightly more.
Density values
Weight (tons) and coverage depend on the bulk density of the stone — how much a cubic foot weighs as delivered. Density varies by stone size, type, and moisture, so we use representative values within commonly cited field ranges and let you override them with a custom density in the calculator. Below is the full reference, grouped by material category. We show both U.S. units (pounds per cubic foot) and the tons-per-cubic-yard figure suppliers quote.
River rock
| Material | Density (lb/ft³) | ≈ Tons / yd³ | Notes |
|---|---|---|---|
| River rock (generic) | 100 | 1.35 | Field range 95–105 lb/ft³ (≈1.3–1.4 t/yd³). |
| 1"–3" river rock | 98 | 1.32 | Larger voids → slightly lower bulk density. |
| 3"–5" river rock | 90 | 1.22 | Large stone, low end of bulk-density range. |
| Crystal river rock | 95 | 1.28 | ≈1,522 kg/m³ converted. |
| Peace river rock | 93 | 1.26 | ≈1,490 kg/m³ converted. |
| Congo river rock | 82 | 1.11 | ≈1,314 kg/m³ converted. |
| Mexican beach pebble | 100 | 1.35 | Smooth, uniform, water-tumbled premium stone. |
Gravel
| Material | Density (lb/ft³) | ≈ Tons / yd³ | Notes |
|---|---|---|---|
| Pea gravel | 105 | 1.42 | Field range 100–125 lb/ft³; compacts dense. |
| Bank gravel | 93 | 1.26 | ≈1,483 kg/m³ converted. |
| Regular gravel | 84 | 1.13 | Low end of range; U.S. dry gravel often 95–105 lb/ft³. |
| Dolomite gravel | 100 | 1.35 | Crushed/lumpy form ≈80–100 lb/ft³. |
| Cheshire pink gravel | 96 | 1.3 | ≈1,545 kg/m³ converted. |
Crushed stone
| Material | Density (lb/ft³) | ≈ Tons / yd³ | Notes |
|---|---|---|---|
| Crushed stone | 100 | 1.35 | Angular; interlocks. ≈1,602 kg/m³. |
| Crushed granite | 93 | 1.26 | Supplier data ≈2,500 lb/yd³ (≈1.25 t/yd³). |
| Decomposed granite | 110 | 1.49 | Higher density; compacts firmly. |
Decorative
| Material | Density (lb/ft³) | ≈ Tons / yd³ | Notes |
|---|---|---|---|
| White marble chips | 89 | 1.2 | Bulk landscape chips; ≈1.20 t/yd³. |
| Lava rock | 50 | 0.68 | Very light & porous; covers more per ton. |
These tables render directly from the calculator's own data, so the published values and the tool can never drift apart. Where published sources disagree on a stone's density (which is common), we use a value near the middle of the credible range and note it.
Coverage figures
The coverage charts elsewhere on the site (square feet per ton and per cubic yard at various depths) are derived from the same formulas using generic river rock at about 100 lb/ft³. Coverage is the inverse of depth: the deeper the layer, the less area a given quantity covers. We present coverage as guidance — your actual coverage depends on the stone size and how evenly it's spread.
Cost ranges
The price ranges on our river rock cost page are typical U.S. ranges for guidance only, not live quotes. Stone pricing varies widely by region, supplier, color, quantity, season, and delivery distance, so we publish ranges rather than single figures and clearly label them as estimates. We review these periodically and date them. Always confirm current pricing with a local supplier before buying — and use the calculator with your own quoted prices for the most accurate total.
Data sources & references
Our density and coverage values reflect commonly published figures from landscape-material suppliers and standard aggregate references, cross-checked against multiple sources to land on representative numbers rather than any single vendor's marketing figure. Where sources disagree (and for stone density they often do), we choose a value near the middle of the credible range and disclose the range in the notes above. Cost ranges are compiled from typical supplier pricing across regions.
How we keep this current
We date every data-sensitive page and revisit the density table and cost ranges on a regular cadence, updating the "last updated" date when we change figures. If you spot a value that looks off for your area, that's expected — local conditions vary — but we welcome corrections that improve the defaults for everyone.
A note on accuracy
Our results are careful estimates, not guarantees. Delivered quantities, stone density, and prices all vary in the real world, which is why we include an overage allowance and present cost as ranges. For a firm quantity and price, confirm with your supplier — and treat our tool as the fast, transparent way to get a reliable starting point.