Rip-Rap Calculator — Erosion Control Stone Volume & Weight
Estimate how many tonnes and cubic metres of rip-rap you need for a slope, streambank, or shoreline protection project. Enter the area dimensions and layer thickness, adjust the as-placed density for your stone type, and add a unit price for an instant material cost estimate.
m
m
m
t/m³
/ tonne
As-placed weight, including voids between stones
15 m³
Rip-rap volume- 1
Volume
10 × 3 × 0.5 = 15 - 2
Weight (tonnes)
15 × 1.7 = 25.5
How does this calculator work?
Multiply the protected area (length × width) by the rip-rap layer thickness to get the volume in m³. Multiply by the as-placed density (typically 1.5–1.9 t/m³; default 1.7 t/m³ for granite) to get the weight in tonnes to order. Always add 5–10% for wastage and irregular terrain.
Formula
How this is calculated
Rip-rap is angular, hard rock — typically granite, basalt or limestone — placed to protect embankments, stream banks, lake shores and spillways from erosion by water and waves. Unlike gravel, it is usually sized by the engineer (D50, D85 stone size criteria) based on the expected hydraulic forces; the layer thickness is typically 1.5× the maximum stone diameter.
The calculator models the protected area as a rectangular block and multiplies length × width × thickness to get the bulk volume to fill. The bulk volume is converted to weight using the as-placed density (also called bulk or placed density), which accounts for the air voids between stones. Typical as-placed density for granite rip-rap is about 1.7 tonnes/m³ — solid granite is ~2.7 t/m³, but the void space between angular stones is roughly 35–40% of the total volume. Limestone or sandstone rip-rap tends to fall toward the lower end of the 1.5–1.9 t/m³ range.
Note: this calculator gives a material quantity estimate only. Proper rip-rap design requires site-specific hydraulic analysis (flow velocity, wave height, D50 stone sizing, filter layer design) and should be performed by a civil or geotechnical engineer for critical structures.
Frequently asked questions
Rip-rap consists of large, angular, durable rocks (typically 150 mm to over 1 m across) placed to resist hydraulic forces. Gravel is smaller, rounder, and used for drainage, surfacing or fill. Rip-rap is specified for erosion protection; gravel would wash away under the same conditions.
A common rule of thumb is that the layer thickness should be at least 1.5× the D50 (median stone size) and preferably 2× D85. Typical installed thicknesses range from 0.3 m for light wave protection to 1.2 m or more for heavy hydraulic loading. Always follow site-specific engineering guidance.
The default 1.7 t/m³ suits most granite or basalt rip-rap as placed with voids. Adjust to ~1.5 t/m³ for softer or more rounded stone, or ~1.8–1.9 t/m³ for dense, well-graded material. Suppliers can provide the as-delivered bulk density for their specific product.
Also known as
TG we-Calculate Editorial Team. (2026). Rip-Rap Calculator — Erosion Control Stone Volume & Weight [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/rip-rap-calculator
TG we-Calculate Editorial Team. "Rip-Rap Calculator — Erosion Control Stone Volume & Weight." TG we-Calculate. 2026. https://we-calculate.com/calculator/rip-rap-calculator.
TG we-Calculate Editorial Team, "Rip-Rap Calculator — Erosion Control Stone Volume & Weight," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/rip-rap-calculator
@misc{wecalculate_rip_rap_calculator, title = {Rip-Rap Calculator — Erosion Control Stone Volume & Weight}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/rip-rap-calculator}}, year = {2026}, note = {TG we-Calculate} }
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