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River Rock Calculator

Ready to calculate
5 Rock Sizes.
Tons + Yards + Bags.
Rect · Circle · Triangle.
100% Free.
Privacy Secure.

How it Works

01Pick Rock Size

Pea (3/8 in), small (1 in), medium (2-3 in), large (4-6 in), boulder (8+ in).

02Shape + Size

Rectangle, circle, or triangle. Enter dimensions in feet.

03Depth

Bed depth in inches. 2 in decorative, 4 in drainage, 6+ dry creek.

04Tons + Cost

Weight in tons + yards, bag count, and total cost at local price.

What is a River Rock Calculator?

A river rock calculator — also called a landscape rock calculator, decorative stone calculator, or dry creek bed calculator — tells you exactly how many tons (or cubic yards) of smooth rounded river stones you need for a landscape bed, dry creek bed, French drain top coat, pond edging, waterfall structure, or xeriscape accent. Every landscape supply yard sells river rock by the ton, but DIYers think in cubic yards or square feet — and estimating by eye almost always under- or over-orders by 30% or more.

This tool uses landscape-yard-verified density data ranging 92-100 lb/ft³ depending on rock size (smaller rocks pack tighter and weigh more per cubic foot than large rocks with more air gaps). It supports five size categories covering the full landscape supply range: pea river rock (3/8-1/2 in) for paths and pool surrounds, small river rock (3/4-1-1/2 in) for drainage and dry creeks, medium river rock (2-3 in) for decorative beds and step stones, large river rock (4-6 in) for statement rocks and pond edges, and boulder river rock (8+ in) for focal points and retaining wall caps.

Three bed shapes are supported: rectangle, circle, and triangle. Enter dimensions in feet, set bed depth in inches (2 in decorative bed, 3-4 in drainage, 6+ in dry creek), pick rock size, and you get tonnage, cubic yards, 50 lb bag count, and total cost with a 10% waste factor baked in.

Default prices reflect 2026 US landscape supply yard averages: pea $55/ton, small $65/ton, medium $75/ton, large $95/ton, boulder $140/ton. Regional pricing varies ±30% — optional custom price override lets you match your local supplier's rate. Delivery fees typically add $30-75 for under 5 tons, often free over 10 tons. Bulk from a landscape supply yard is always 2-3× cheaper than bagged river rock at a big-box store.

How the River Rock Calculator Works

Bed area: rectangle (L × W), circle (π r²), or triangle (½ × base × height) in ft².
Volume = Area × depth_in / 12. Typical depths: 2 in decorative bed, 3-4 in drainage cap, 6+ in dry creek bed.
Weight = Volume × density (lb/ft³). Pea/small/medium rock density 95-100 lb/ft³. Large and boulder rocks 92-95 lb/ft³ (more air gaps due to size).
Tons = Weight / 2,000. River rock is sold by the ton at landscape yards, not by the yard.
Cost = Tons × price/ton. Default prices $55-140/ton depending on size. 10% waste baked in.

River Rock Formula

Area × depth × density gives weight; divide for tons:

Area_ft² = depends on shape
  Rectangle: L × W
  Circle: π × (D / 2)²
  Triangle: 0.5 × B × H
Volume_ft³ = Area_ft² × (depth_in / 12) × 1.10 (waste)
Weight_lb = Volume_ft³ × Density_lb/ft³
Tons_US = Weight_lb / 2,000
Cost = Tons × Price_per_ton
Density by rock size:
  Pea 3/8 in:    95 lb/ft³
  Small 1 in:    100 lb/ft³
  Medium 2-3 in: 100 lb/ft³
  Large 4-6 in:  95 lb/ft³
  Boulder 8 in+: 92 lb/ft³
Real-World Example

Worked Example

A decorative 20 × 8 ft rectangular bed of medium river rock (2-3 in), 3 inches deep:

  • Area = 20 × 8 = 160 ft²
  • Volume = 160 × (3/12) × 1.10 = 44 ft³
  • Cubic yards = 44 / 27 = 1.63 yd³
  • Weight = 44 × 100 lb/ft³ = 4,400 lb = 2.20 tons
  • Cost at $75/ton = $165 before delivery ($40-60 local).
  • Bagged (50 lb) alternative = 88 bags at $5/bag = $440. Bulk wins by more than 2×.

Who Uses This Calculator?

1
Homeowners installing decorative front/side yard beds and dry creek beds
2
Landscape designers pricing xeriscape projects and gravel gardens
3
Pond and water-feature installers sizing edge rock and waterfall fill
4
Drainage contractors capping French drains and swales with decorative rock
5
DIY gardeners replacing mulch with low-maintenance rock beds

Technical Reference

AASHTO M43 — standard sizing for aggregate stone (ASTM sieve designations). River rock is washed and rounded rather than crushed, but uses the same nominal sizes.

Density reference — 95-100 lb/ft³ (1,525-1,600 kg/m³) typical for washed river rock. Crushed stone runs higher (100-110 lb/ft³) due to angular packing.

Key Takeaways

River rock density varies by size because bigger rocks leave more air gaps between them — pea gravel packs tight at 95-100 lb/ft³ while boulders have 10-15% voids at 92 lb/ft³. Bulk from a landscape yard is always the cheapest path: 3× cheaper per ft² than bagged at big-box stores, with free delivery often included over 10 tons. For drainage applications, use 1 inch rock or larger — pea gravel silts up and defeats the drain. For pure decorative beds, 2-3 inch medium river rock is the Instagram standard: big enough to look intentional, small enough to not shift underfoot. Boulder-size rocks (8+ inches) are usually sold individually rather than by the ton — ask your supplier about accent-boulder pricing. Always install professional-grade landscape fabric (4-6 oz woven, not bargain spunbond) under any river rock bed — extends weed-free life from 1 year to 5+ years.

Frequently Asked Questions

How much does a cubic yard of river rock weigh?
About 2,550-2,700 lb (1.25-1.35 US tons) depending on rock size. Pea and small river rock pack tighter (~2,700 lb/yd³). Large and boulder rocks leave more air gaps (~2,500 lb/yd³).
How many tons of river rock for 100 square feet?
Depends on depth. At 2 inches: 0.83 tons. At 3 inches: 1.25 tons. At 4 inches: 1.67 tons. At 6 inches: 2.50 tons. Budget 2-3 inches for typical decorative beds.
What size river rock is best for landscaping?
2-3 inch medium river rock is the most popular for decorative beds — big enough to look intentional, small enough to not shift underfoot. 1 inch small for paths and drainage. 4-6 inch large for accents and pond edges.
How deep should a river rock bed be?
Minimum 2 inches for complete coverage (with weed fabric underneath). 3-4 inches is typical for decorative beds. 6+ inches for dry creek beds and drainage swales.
How much does river rock cost per ton?
US average: $55-140/ton at the yard depending on size. Pea: $45-65. Small 1 in: $55-75. Medium 2-3 in: $65-85. Large 4-6 in: $85-120. Boulder 8 in+: $110-160. Delivery adds $30-75.
Is river rock better than mulch?
Trade-offs. Rock lasts forever (mulch rots in 2-3 years), reflects heat (mulch insulates), and doesn't wash away (mulch floats). Mulch retains moisture better, feeds soil as it decomposes, and is cheaper upfront. Rock costs more initially but is a one-time install.
Do I need landscape fabric under river rock?
Yes — weed fabric (professional-grade, not cheap spunbond) extends the weed-free life of a rock bed from 1 year to 5+ years. Use 4-6 oz woven fabric with overlap seams, not the $5 bargain roll.
How many 50 lb bags of river rock per ton?
40 bags per ton (2,000 lb / 50 lb). Bagged is 2-3× the cost of bulk — OK for under 500 lb projects, wasteful for anything larger.
Can I walk on river rock?
Yes, for paths use 1 inch small river rock (compacts well). 2-3 inch medium is uncomfortable to walk on barefoot but fine with shoes. Avoid large river rock on paths — ankle twisters.
How do I stop river rock from sinking into the soil?
Install landscape fabric, then a 1-2 inch base layer of crushed stone or decomposed granite, then the river rock on top. Raw rock on bare soil sinks 20-30% into the ground within a year.

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Disclaimer

Educational reference. Regional pricing varies ±30%. Always confirm with your local supplier before ordering.