River Rock Calculator — Tons, Cubic Yards and True Coverage for 1–6 in Decorative Rock
Estimate tons and cubic yards of river rock by stone size — with a size-aware density (1 in vs 6 in pack very differently) and a surface-irregularity allowance that stops the 25% under-order most landscape estimates hit on 2–4 in rock.
River Rock Calculator
Enter project dimensions below — results update instantly. Switch units freely.
Estimates assume typical industry density and waste factors. Always verify with your supplier and local building code before purchasing material.
Why a 100 lb/ft³ Gravel Calculator Under-Orders River Rock by 15–25%
River rock is the trickiest decorative aggregate to estimate because density falls as stone size grows. A 1-in rounded river pebble packs at ~95 lb/ft³ (close to standard gravel). A 4-in cobble packs at ~80 lb/ft³ because the voids between the rocks are huge. Use a generic gravel calculator at 100 lb/ft³ on a 3-in dry creek bed and you’ll order 15–20% short before you even factor in the surface bumpiness.
The other miss most online calculators make: they assume the placed depth equals the ordered depth. With 2–4 in rounded stone, that’s only true at perfectly flat finished grade. In a real dry creek bed or landscape feature, you need 5–25% extra material to ride the high spots and fill the low spots — the surface-irregularity allowance. The calculator above splits this out as ‘Coverage Adjust’ so the order tons reflect what your truck driver actually has to dump.
Three places river rock estimates go wrong:
- Wrong density for the stone size — 1–2 in vs 4–6 in is a 15 lb/ft³ spread. Order from the wrong column and you’re a quarter-ton short on every yard.
- No surface-irregularity allowance — large rounded stones sit proud of the design grade; you need 15–25% more material to get a level visual finish.
- French-drain caps using the wrong stone — large river rock looks great on top, but the drainage layer below has to be #57 angular clean stone, not river rock. The pillar page goes through the layer stack.
How to Calculate River Rock Calculator
ft³order = ft³base × coverage adjust × (1 + waste%)
Tons to Order = (ft³order × size-density) ÷ 2000
Two corrections the standard gravel formula skips: size-density (95 lb/ft³ for 1 in → 80 lb/ft³ for 6 in) and coverage adjust (1.05 small stone → 1.25 large stone). Both are visible inputs in the calculator above so you can match supplier’s product data.
Stone-Size to Density & Coverage Adjust
| Nominal size | Loose density | Coverage adjust | Tons/yd³ | Best use |
|---|---|---|---|---|
| 3/4–1 in | 95 lb/ft³ | 1.05 | 1.28 | French-drain cap, decorative top dressing |
| 1–2 in | 90 lb/ft³ | 1.10 | 1.22 | Walkways, drainage swales, ground cover |
| 2–4 in | 85 lb/ft³ | 1.15 | 1.15 | Dry creek beds, xeriscape, feature beds |
| 4–6 in | 80 lb/ft³ | 1.20 | 1.08 | Boulder accent, retaining wall fill, large-scale landscape |
| 6–12 in (cobble) | 78 lb/ft³ | 1.25 | 1.05 | Solo placement, water-feature edging, slope erosion |
Depth-by-Application
- Dry creek bed — 4–6 in depth with 1–2 in border stones graduating to 4-in ‘water-line’ stones in the centerline. Pre-line with 4-oz landscape fabric over a 6-in compacted base.
- Mulch alternative (xeriscape bed) — 2–3 in depth, 1–2 in rock. Lay weed fabric below; expect to refresh top dressing every 3–5 years.
- French-drain top cap (over #57 stone bedding) — 4–6 in of 1–2 in river rock; the cap is decorative and protects the drain stone from clogging with leaf litter.
- Landscape feature / accent — 3–4 in depth, 2–4 in stone. The depth has to bury at least the bottom 60% of a stone for it to read as ‘river-bed natural.’
- Slope erosion control — 6–12 in depth, 4–6 in stone. Use only on slopes flatter than 1:2; steeper needs riprap with toe trench.
Pair the river rock with the Crushed Stone Calculator for the drainage stone underneath (#57 clean), or the Pea Gravel Calculator for the fine top layer between feature stones. For French-drain bedding spec, see the Crushed Stone Calculator.
River Rock Coverage Table and Material Reference
| Depth | ft² per ton | ft² per yd³ | Tons per 100 ft² |
|---|---|---|---|
| 2 in | 123 ft² | 141 ft² | 0.81 tons |
| 3 in | 82 ft² | 94 ft² | 1.22 tons |
| 4 in | 61 ft² | 70 ft² | 1.63 tons |
| 5 in | 49 ft² | 56 ft² | 2.04 tons |
| 6 in | 41 ft² | 47 ft² | 2.45 tons |
| 8 in | 31 ft² | 35 ft² | 3.26 tons |
| 12 in | 20 ft² | 23 ft² | 4.90 tons |
Coverage for 2–4 in river rock at 85 lb/ft³ with 1.15 coverage adjust and 5% waste. Smaller stone (1-in) covers ~10% more area per ton; larger stone (4–6 in) covers ~10% less.
| Stone size | Price/ton | Coverage at 3 in | Cost per 100 ft² at 3 in |
|---|---|---|---|
| 3/4–1 in | $45 | 91 ft²/ton | $49 |
| 1–2 in | $55 | 86 ft²/ton | $64 |
| 2–4 in | $65 | 82 ft²/ton | $79 |
| 4–6 in | $80 | 77 ft²/ton | $104 |
| 6–12 in (cobble) | $110 | 65 ft²/ton | $169 |
Bulk delivered prices, 2026 Mid-Atlantic baseline within 20 miles of quarry. Larger sizes cost more per ton and cover less area per ton — both work against your budget. For most decorative-bed jobs, 1–2 in is the value sweet-spot.
Real-World Example Calculations
Dry Creek Bed 20 ft × 4 ft, 4 in average depth, 2 in river rock
Backyard drainage feature with naturalistic look; weed fabric over 6-in compacted base.
- L × W
- 20 × 4 ft = 80 ft²
- Depth
- 4 in average
- Rock size
- 2 in (uses 90 lb/ft³, 1.10 coverage adjust)
Takeaway: Single half-ton pickup-truck load or quarry minimum 1-ton delivery. Order the 1–2 in size for ground cover; pick a few 4–6 in ‘feature’ stones separately for the centerline waterline (about 4–6 stones).
Xeriscape Bed 30 ft × 10 ft, 3 in, 1–2 in river rock
Front-yard drought-tolerant bed replacing lawn; landscape fabric below, edging on three sides.
- L × W
- 30 × 10 ft = 300 ft²
- Depth
- 3 in
- Rock size
- 1–2 in (90 lb/ft³, 1.10 adjust)
Takeaway: Two pickup-truck deliveries or one tri-axle. Expect to top-dress with another half-ton in years 3–5 as the rock settles into the soil below.
French Drain Cap 50 ft × 2 ft, 6 in, 1 in river rock
Top decorative cap over an existing French drain (drain stone underneath is #57 clean, not river).
- L × W
- 50 × 2 ft = 100 ft²
- Depth
- 6 in
- Rock size
- 1 in (95 lb/ft³, 1.05 adjust)
Takeaway: Single delivery. Use 1 in (not 2–4 in) so leaf litter doesn’t sit in the voids and clog the drain bed below.
Sources & Standards
These references are used for terminology, safety boundaries, and engineering assumptions. Local code, supplier specifications, and licensed design documents still control your project.
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ASTM D448 — Standard Classification for Sizes of Aggregate for Road and Bridge Construction
ASTM International
Referenced for sizing nomenclature crossing decorative river rock with construction-aggregate gradation (#3, #4, #467 envelopes).
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USDA NRCS Engineering Field Handbook — Chapter 16: Streambank and Shoreline Protection
USDA Natural Resources Conservation Service
Referenced for riprap and dry-creek-bed stone-sizing guidance: D50 stone-size selection by flow velocity, channel slope, and erosion risk.
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Xeriscape Conversion Study — Southern Nevada Water Authority
Southern Nevada Water Authority
Referenced for typical xeriscape rock-mulch depths (2–3 in over fabric) and water-savings impact data.
Frequently Asked Questions
How much river rock do I need per square foot?
For 2–4 in river rock at 3 in depth: 1 ton covers ~82 ft². For a 200 ft² bed at 3 in deep, order 2.44 tons (round up to 2.5). Smaller stone covers more area per ton; larger stone covers less.
How many tons of river rock in a cubic yard?
Depends on size: 1–2 in stone is 1.22 tons/yd³; 2–4 in is 1.15 tons/yd³; 4–6 in is 1.08 tons/yd³. Larger rocks have more void space between them, so tons-per-yard drops as size grows.
How deep should river rock be in a landscape bed?
2–3 inches for a mulch-alternative bed (with weed fabric below); 3–4 inches for a decorative feature (you need to bury at least the bottom 60% of stones to look natural); 4–6 inches for dry creek beds and drainage swales.
What size river rock is best for landscaping?
1–2 inch is the value sweet-spot for general landscape beds, walkway borders, and ground cover. Step up to 2–4 in for dry creek beds and feature areas. Use 4–6 in only as an accent (4–6 individual stones placed deliberately) — covering a whole bed in 4–6 in cobble looks rocky-quarry, not naturalistic.
How much does river rock cost per ton in 2026?
2026 Mid-Atlantic bulk-delivered baseline: $45/ton for 3/4–1 in, $55/ton for 1–2 in, $65/ton for 2–4 in, $80/ton for 4–6 in, $110/ton for cobble (6–12 in). Plus typical $85 delivery fee within 20 miles. Bagged retail runs 3–4× the bulk price — buy bulk for any order above 1 ton.
Can I use river rock in a French drain?
Only as a top cap, not for the drainage layer itself. The drainage layer needs #57 angular clean stone so water flows freely through the perforated pipe; rounded river rock packs too tight and slows percolation. Cap the top 4–6 inches with 1 in river rock for the decorative finish.
Does river rock need landscape fabric below it?
Yes for landscape beds and walkways (4-oz woven fabric blocks weeds and stops rocks sinking into soil). No for dry creek beds and drainage features — you want water to percolate through. No under French-drain caps — the drainage layer below already has fabric wrapping the perforated pipe.