River Rock Calculator
Enter the area dimensions and desired depth, choose your rock type, and this calculator returns the volume in cubic yards and cubic feet, the weight in tons and pounds, a cost estimate, and the number of bags if you are buying in bags. Switch between imperial and metric units, add a waste percentage so you never run short, and see the full worked calculation. Results update as you type.
How to calculate river rock coverage
The basic formula is: volume (cubic feet) = area (sq ft) x depth (ft). Divide by 27 to convert to cubic yards, then multiply by the bulk density of your chosen rock (typically 1.30-1.60 tons per cubic yard for river rock) to get the weight in tons. This calculator handles all the unit conversions for you, whether you are working in feet and inches or metres and centimetres. For most landscape beds, a depth of 2-3 inches is standard. For dry creek beds, drainage swales, or paths that see foot traffic, use 4-6 inches. Larger cobbles (3-5 inch stones) need more depth because individual rocks leave air gaps, so the effective coverage per ton is lower than for fine pea gravel.
Why bulk density matters, and how it varies
River rock is sold by weight (tons) but you need to know how much space it will fill (cubic yards). The conversion factor is the bulk density: how many tons fit in one cubic yard of loosely piled rock. Fine pea gravel (3/8 inch) packs more tightly and weighs around 1.40 tons per cubic yard. Large cobbles (4-5 inch) leave more air space and weigh closer to 1.30 tons per cubic yard. Crushed or angular stones pack tighter than round river rocks and can reach 1.55-1.60 tons per cubic yard. Always ask your supplier for the exact bulk density of the specific material they stock, because the same product name can vary by quarry. For a standard decorative river rock project the calculator default of 1.35 tons per cubic yard is a safe middle estimate.
Waste allowance: how much extra to order
Always order more than your bare calculation suggests. A 10% waste allowance is standard for simple rectangular beds. Increase it to 15-20% for irregularly shaped areas, beds with lots of obstacles (plants, stepping stones), or slopes where rock can slide and shift. Add an extra 5-10% if you are covering a dry creek bed, as the uneven channel profile means more rock per linear foot than a flat calculation implies. Ordering extra is far cheaper than a second delivery, which usually carries a minimum charge. If you have a small overage, river rock stores well uncovered and can be used to top off thin spots after the first winter.
Bulk delivery vs. bagged river rock
Bulk delivery is almost always more economical for projects over 1 cubic yard (about 1.35 tons or 27 cubic feet). Bagged river rock from a home improvement store typically costs 3-5 times more per ton than bulk stone, but bagged products are convenient for small repairs, tight-access areas, or when you want a specific decorative stone not available in bulk. A standard 50 lb bag covers about 2 square feet at 2 inches deep. You would need roughly 13-14 bags to cover 100 square feet at that depth, compared to buying about 0.19 tons in bulk. At $150-$200 per ton for bulk stone vs. $6-$12 per 50 lb bag retail, the savings on a 500 sq ft project can be $300 or more.
River rock coverage by size and bulk density
| Rock size | Bulk density (tons/yd³) | Coverage at 2" depth (sq ft/ton) | Common uses |
|---|---|---|---|
| 3/8 inch (pea gravel) | 1.4 | 100-120 | Paths, playgrounds, small borders |
| 1/2-1 inch (small) | 1.35 | 85-100 | Flower beds, ground cover |
| 1-2 inch (medium) | 1.35 | 75-90 | Garden borders, mulch replacement |
| 2-3 inch (large) | 1.35 | 60-80 | Dry creek beds, drainage |
| 3-5 inch (extra large) | 1.32 | 50-65 | Water features, retaining walls |
| 5+ inch (cobble) | 1.3 | 40-55 | Landscape accents, pond edges |
Approximate coverage at 2-inch depth and typical bulk density by stone size. Actual coverage depends on supplier and compaction.
Frequently asked questions
How many cubic yards of river rock do I need for a 10 x 10 area?
For a 10 x 10 foot area (100 sq ft) at a 2-inch depth: 100 x (2/12) / 27 = 0.62 cubic yards. At a 3-inch depth you need 0.93 cubic yards. This calculator works out the exact figure for any dimensions and depth, and adds your chosen waste buffer automatically.
How many tons is a cubic yard of river rock?
Standard decorative river rock weighs approximately 1.30-1.40 tons per cubic yard. The exact value depends on stone size and shape: fine pea gravel is around 1.40 tons/yd3, medium river rock (1-3 inch) is about 1.35 tons/yd3, and large cobbles (4-5 inch) can be as low as 1.30 tons/yd3 because the gaps between stones are larger. Crushed or angular stone packs tighter and can reach 1.55-1.60 tons/yd3.
How deep should I lay river rock?
For decorative ground cover in flower beds: 2-3 inches is standard and sufficient to suppress weeds. For walkways and paths that see light foot traffic: 3-4 inches provides a stable surface. For drainage applications, dry creek beds, or retention areas: 4-6 inches or more ensures adequate water flow and structural stability. Larger stones (3-5 inch cobbles) generally need a deeper layer because the gaps between stones mean thinner layers look sparse.
How many square feet does a ton of river rock cover?
At 2 inches deep, one ton of medium river rock covers approximately 75-100 square feet. At 3 inches deep, that same ton covers roughly 50-67 square feet. Coverage varies with stone size: fine pea gravel covers more ground per ton (100-120 sq ft at 2 inches) because it packs tighter, while large cobbles cover less (50-65 sq ft) because of the larger air gaps.
Should I put landscape fabric under river rock?
Landscape fabric under river rock is recommended for decorative beds and weed suppression. It prevents the rock from sinking into soft soil over time and greatly reduces weed growth. For drainage swales and dry creek beds, fabric can sometimes restrict water flow, so check with your local landscaping supplier. Avoid plastic sheeting, which prevents air and water movement and can kill plant roots in adjacent areas.