River Rock Calculator — Volume, Weight & Cost
Find out how many tonnes and cubic metres of river rock your project needs. Enter the area dimensions and depth of the stone layer, adjust the bulk density for your specific stone size, and optionally add a price per tonne for a cost estimate.
Units
m
m
cm
t/m³
/ tonne
As-placed weight including voids between stones
1.2 m³
Rock volume- 1
Volume
5 × 3 × 0.08 = 1.2Depth converted from cm to m (× 0.01). - 2
Weight (tonnes)
1.2 × 1.4 = 1.68
How does this calculator work?
Multiply the covered area's length × width × depth (all in metres) for the volume. Multiply by about 1.4 t/m³ — typical as-placed density for rounded river rock with voids — for the weight to order. Order 10–15% extra for settling and waste.
Formula
How this is calculated
River rock — smooth, rounded stones shaped by water — is popular for garden beds, pathways, drainage trenches, dry creek beds and decorative mulch alternatives. Unlike angular crushed stone, the rounded shape creates larger void spaces when stones are piled together, giving river rock a lower as-placed bulk density (typically 1.3–1.6 t/m³) compared with crushed gravel (1.4–1.7 t/m³) or rip-rap (1.5–1.9 t/m³).
The calculator multiplies the length, width and depth of the area to get the bulk volume to fill, then multiplies by the as-placed bulk density (which already accounts for the air voids between stones) to give the weight you actually order. All dimensions are converted to metres internally — imperial values are multiplied by the standard foot-to-metre or inch-to-metre factor. The result is also shown in cubic yards and US short tons for suppliers who use those units.
For a decorative landscape layer, 5–8 cm (2–3 inches) is typical; for a dry creek bed or drainage application, 10–20 cm (4–8 inches) is common. Order 10–15% extra to account for settling, irregular ground and edges. Stone size affects coverage: smaller pebbles (20–40 mm) fill gaps better; larger cobbles (100–200 mm) need a deeper layer.
Frequently asked questions
For a decorative garden bed or pathway, 5–8 cm (2–3 in) is usually enough to cover soil and suppress weeds. For a dry creek bed or drainage application, use 10–20 cm (4–8 in). Larger stones need a proportionally deeper layer to look intentional.
As placed, river rock typically weighs 1.3–1.6 tonnes per cubic metre — less than crushed gravel because the rounded shape creates larger air voids. Smaller pebbles pack more densely (toward 1.5–1.6 t/m³); large cobbles are toward 1.3–1.4 t/m³.
Yes — river rock will not decompose, does not attract pests and works well around trees and shrubs in arid or fire-prone areas. The trade-off is that it does not add nutrients to the soil and can heat the ground significantly in summer. Organic mulch is generally preferred for vegetable gardens.
Also known as
TG we-Calculate Editorial Team. (2026). River Rock Calculator — Volume, Weight & Cost [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/river-rock-calculator
TG we-Calculate Editorial Team. "River Rock Calculator — Volume, Weight & Cost." TG we-Calculate. 2026. https://we-calculate.com/calculator/river-rock-calculator.
TG we-Calculate Editorial Team, "River Rock Calculator — Volume, Weight & Cost," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/river-rock-calculator
@misc{wecalculate_river_rock_calculator, title = {River Rock Calculator — Volume, Weight & Cost}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/river-rock-calculator}}, year = {2026}, note = {TG we-Calculate} }
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