River Rock Calculator
River rock sells by the cubic yard or by the bag, but your project is measured in square feet and depth. This calculator bridges that gap — converting your coverage area into cubic yards, tons, bags, and total cost for decorative and drainage projects.
Quick Reference
River Rock Types Compared
River rock comes in various sizes for different applications. Here is a comparison to help you choose the right type for your project:
| Type | Weight (lbs/ft³) | Tons/Yard³ | Best For | Typical Price/yd³ |
|---|---|---|---|---|
| River Rock (1-2") | 93 | 1.25 | Decorative ground cover, garden beds | $50-$80 |
| River Rock (2-4") | 93 | 1.25 | Drainage, dry creek beds, borders | $70-$100 |
| River Rock (4-6") | 93 | 1.25 | Heavy drainage, erosion control | $80-$110 |
| Large Decorative | 93 | 1.25 | Feature accents, water features | $90-$130 |
River Rock Depth Guide
Depth depends on your project. Too thin and it will not provide adequate coverage or drainage. Too deep and you waste money.
| Depth | Best For | Sq Ft per Ton |
|---|---|---|
| 2 inches | Decorative ground cover, garden beds | ~144 sq ft |
| 3 inches | Borders, pathways, tree wells | ~96 sq ft |
| 4 inches | Drainage areas, downspout extensions | ~72 sq ft |
| 6 inches | French drains, dry creek beds, erosion control | ~48 sq ft |
River Rock vs Mulch: Which Do You Need?
River rock and mulch serve different purposes. Here is when to use each:
Use River Rock When
- Creating drainage solutions
- Building dry creek beds
- Covering areas that stay wet
- Decorating around water features
- Low-maintenance ground cover
- Erosion-prone slopes
Use Mulch When
- Covering garden beds and shrubs
- Retaining soil moisture for plants
- Adding organic matter to soil
- Creating play areas for children
- Suppressing weeds in planted areas
- Insulating plant roots for winter
How to Use This Calculator
Step 1: Choose your area shape - Rectangle for standard areas, Circle for tree wells or round features, or Total Area if you already know the square footage.
Step 2: Enter dimensions. For rectangle, enter length and width. For circle, enter diameter. For total area, enter square footage directly.
Step 3: Set depth using the preset buttons (2"-6") or enter a custom value.
Step 4: Enter pricing. The calculator shows bulk vs bag cost comparison.
Step 5: Results show instantly - tons, cubic yards, bag count, cost breakdown, and total.
River Rock Formula
The calculator converts your project dimensions into river rock volume and cost:
- Rectangle: Area = Length x Width
- Circle: Area = Pi x (Diameter / 2)²
- Volume (ft³) = Area (ft²) x (Depth in inches / 12)
- Volume (yd³) = Volume (ft³) / 27
- Tons = Volume (ft³) x 93 / 2,000
- Bags (0.5 ft³) = Volume (ft³) / 0.5
- Bulk Cost = Volume (yd³) x Price per Cubic Yard
- Bag Cost = Bags x Price per Bag
River rock weighs 93 lbs per cubic foot (2,500 lbs per cubic yard). This is heavier than sand due to the density of natural stone. The calculator uses a fixed density of 93 lb/ft³ for all river rock sizes.
Worked Example: 15x10 Garden Bed
Let us calculate river rock for a 15 ft x 10 ft garden bed at 2 inches deep with 10% waste at $90/yd³.
Step 1: Calculate volume:
Volume = 150 x (2 / 12) = 25 ft³
Cubic Yards = 25 / 27 = 0.93 yd³
Step 2: Calculate weight:
Tons = 2,325 / 2,000 = 1.16 tons
Step 3: Calculate cost at $90/yd³:
Bags = 25 / 0.5 = 50 bags x $12 = $600
Total: 0.93 cubic yards of river rock at $83.93 bulk vs $600 bagged. Use the calculator above to model your own project.
Tips and Common Mistakes
Best Practices
- Use landscape fabric - Prevents weeds and keeps rock from sinking into soil.
- Order 10% extra - River rock settles and shifts; extra covers uneven spots.
- Match rock size to application - 1-2" for decor, 2-4" for drainage, 4-6" for heavy drainage.
- Compare bulk vs bags - Bulk is almost always cheaper for projects over 1 cubic yard.
- Consider depth carefully - 2" for ground cover, 3-4" for drainage areas.
Avoid This
- Skipping landscape fabric: Weeds will grow through and rocks sink into soil over time.
- Using too shallow a layer: Less than 2 inches looks sparse and does not suppress weeds.
- Ignoring drainage needs: Flat areas need proper grading underneath to prevent pooling.
- Ordering too little: Running out mid-project means a second delivery fee.
- Mixing rock sizes: Different sizes settle unevenly and look inconsistent.
Frequently Asked Questions
A 0.5 cubic foot bag of river rock covers about 3 sq ft at 2 inches deep. For 1 cubic yard (27 cubic feet), you need about 54 bags. For smaller projects, calculate cubic feet needed and divide by 0.5.
River rock costs $50-$130 per cubic yard in 2026. Smaller 1-2 inch river rock runs $50-$80, medium 2-4 inch rock costs $70-$100, and larger decorative river rock reaches $80-$130 per cubic yard.
River rock weighs about 2,500 lbs per cubic yard (93 lbs per cubic foot). This is heavier than sand due to the density of natural stone.
For decorative ground cover, 2 inches is standard. For drainage areas and dry creek beds, use 3-4 inches. For heavy drainage or French drains, 4-6 inches provides adequate water flow.
Yes, landscape fabric is highly recommended. It prevents weeds from growing through, keeps river rock from sinking into the soil, and makes future maintenance easier. Use commercial-grade woven fabric.
Yes, river rock is excellent for drainage. Its rounded shape creates natural gaps for water flow. Use 2-4 inch river rock in French drains, around downspouts, and in dry creek beds for effective water management.