How to use the river rock calculator
- Enter the area of the bed as a rectangle or circle.
- Choose the rock size. Leave depth blank to use an automatic depth of about twice the average stone size, or enter your own.
- Adjust density if your supplier gives a different figure, and add a small extra allowance.
- Optionally enter a price per ton, per cubic yard or per bag.
How the calculation works
Decorative rock needs to be deep enough that stones overlap and cover the soil or landscape fabric. A common landscaping guideline is a depth of roughly twice the average stone diameter, so larger rock needs a deeper layer and more tons per square foot.
Volume is area × depth plus the allowance; tons = cubic yards × density. Coverage per ton shows how many square feet one ton covers at your depth, which is handy when a supplier sells by the ton.
Formula
Worked example
12 × 6 ft bed of 1-3 in rock
Auto depth = 2 × 2 in = 4 in. Volume = 72 × (4 ÷ 12) = 24 ft³ = 0.889 yd³; with 5% extra 0.933 yd³.
Weight at 1.35 tons/yd³ = 1.26 tons, or about 57 sq ft per ton.
Assumptions and limitations
- The depth rule of thumb is a guideline. Slopes, drainage swales and dry creek beds may need more rock or larger stones.
- Rock density varies with stone type and size; ask the supplier for their tons-per-yard figure.
- Landscape fabric, edging and delivery are not included in the cost.
Frequently asked questions
How many square feet does a ton of river rock cover?
It depends on depth. At 1.35 tons/yd³, a ton covers about 120 sq ft at 2 in deep, 80 sq ft at 3 in, and 60 sq ft at 4 in.
How deep should river rock be?
Usually 2-3 in for small rock and 4-6 in or more for larger stones, roughly twice the stone size.
How is this different from the pea gravel calculator?
River rock comes in much larger sizes, so this tool ties depth to stone size and reports coverage per ton. The pea gravel calculator focuses on bag counts for small, uniform stone.