River Rock & Decorative Stone Calculator
Work out how much river rock or decorative stone you need in cubic yards and tons from your area, depth and stone density.
Calculator
River rock or decorative stone over 150 sq ft at 3.0 in is about 1.39 cu yd (~1.94 tons). Larger stone needs a bit more depth to cover the ground fully; density is a labeled typical — confirm with your supplier.
River rock, lava rock and other decorative stone give beds and borders a clean, low-maintenance finish that does not break down like mulch. The quantity is the same area×depth geometry, converted to cubic yards and then to a weight in tons — decorative stone is usually delivered by the yard but priced by the ton. Pick the density that matches your stone; river rock runs about 1.4 tons per cubic yard.
Because stone stays put, many homeowners lay it over landscape fabric for weed control. For a hardscape base or a drainage-free gravel path, see the gravel calculator.
Formula
Decorative stone follows the bulk-material formulas:
cubic yards = area (sq ft) × depth (in) ÷ 324
tons = cubic yards × density (tons per cu yd)
The 324 constant converts square-feet-inches to cubic yards. Larger, rounded stone has more air gaps and needs a deeper layer to hide the ground; density (about 1.4 tons per cubic yard) is a labeled typical, so confirm the real weight with your supplier.
Worked example
For a 150 sq ft bed at 3 in in river rock (1.4 t/cu yd):
- Volume:
150 × 3 ÷ 324 = 1.39 cu yd - Weight:
1.39 × 1.4 = 1.94 tons
So the bed takes about 1.39 cubic yards of stone, roughly 1.94 tons.
Laying decorative stone
Decorative-stone tips:
- Depth by stone size. Small pea gravel covers at 2 in; 2–4 in river rock needs 3–4 in to fully hide the soil beneath.
- Fabric first. Landscape fabric under the stone slows weeds and keeps the rock from sinking into the soil.
- Edge it. Steel, stone or plastic edging keeps decorative rock in the bed and out of the mower’s path.
- Buy by weight, plan by volume. Confirm the tons-per-yard for your specific stone, then price the load with the bulk-material cost calculator.
Reference table
Volume and approximate weight per 100 sq ft at 1.40 tons per cubic yard (density is a labeled typical — confirm it with your supplier):
| Depth | Cubic yards | Tons |
|---|---|---|
| 2 in | 0.62 cu yd | 0.86 tons |
| 3 in | 0.93 cu yd | 1.30 tons |
| 4 in | 1.23 cu yd | 1.73 tons |
| 6 in | 1.85 cu yd | 2.59 tons |
More densities on the gravel & stone density table.