Riprap Calculator
Estimate riprap rock volume and weight for erosion-control layers in imperial or metric units, with adjustable bulk density and ordering allowance.
Add 5–10% for waste and uneven ground; default 10%.
Typical placed bulk density: approximately 1,600–2,200 kg/m³ depending on rock type, size distribution and voids. Default: 1,800 kg/m³.
About the Riprap Calculator
Riprap consists of large rock placed to protect banks, drainage channels and other surfaces from erosion. Enter the actual surface length, width and rock-layer thickness to estimate volume. For a slope, measure along the slope rather than using only its horizontal projection; otherwise the protected surface area will be underestimated.
Bulk density includes void space between stones and is not the same as solid-rock density. A practical planning range is roughly 1.6–2.2 metric tonnes per cubic meter, with 1.8 used here by default. A 10 m by 2 m surface covered 30 cm deep occupies 6 m³; with 10% allowance it needs 6.6 m³, about 11.88 tonnes at 1,800 kg/m³.
Rock sizing, layer thickness, filter fabric and hydraulic stability require a project-specific design; this quantity estimator does not assess erosion resistance. For smaller drainage aggregate use the Gravel Calculator. The Sand Calculator estimates a separately specified sand layer, while the Concrete Calculator applies to concrete works. Keep US short tons and metric tonnes distinct when requesting delivery quotes.
Frequently Asked Questions
Which riprap density should I choose?
Use the supplier or design specification when available. The default is 1,800 kg/m³; typical bulk estimates of 1,600–2,200 kg/m³ reflect different rock types, grading and voids.
Can this design erosion protection?
No. It estimates material quantity only. Flow conditions, slope stability, filter layers and suitable rock size need a site-specific design.
How should I measure a sloped bank?
Use the actual along-slope surface length and width, with thickness measured normal to that surface. Split irregular shapes into simpler areas and total their estimates.
Take this calculation further
Browse the other calculators collection for more tools in this subject.
For a related calculation, use Concrete Calculator to calculate concrete volume in cubic feet and yards for slabs, cylinders, and footings. Find bags needed. Alternatively, use Paver/Patio Base Calculator to estimate construction gravel sub-base and sand bedding together using independent layer depths and metric or imperial units.