USDOT/Caltrans gradation classes, void ratio & bedding layers
For slopes, use the slope (surface) length, not the horizontal run.
Larger armor stone classes carry a higher void ratio and need a proportionally thicker placed layer to fully interlock and resist scour.
Dumped riprap settles randomly with more open void space. Hand-placed or chinked (wedged/interlocked) stone packs tighter, reducing void space and effective volume needed for the same coverage weight.
⚠️ Layer may be too thin for this gradation class
Void Space in Placed Layer
Void ratio adjusts with both gradation class and placement method this is the open space between armor stones after placement, relevant to underlying filter design and scour potential.
A choke stone layer (#57 stone or dense-graded aggregate base) prevents underlying soil from washing up through the void space in the riprap above it. Calculated separately from the armor stone since it uses a different material and density.
Heavy armor stone requires heavy-duty non-woven filter fabric (much higher puncture resistance than standard landscape fabric) to survive placement without tearing.
Please enter valid dimensions first.
Armor Stone Needed
–US tons
Enter your project details and calculate to see results.
Estimate Your Cost
Armor stone cost only pre-filled around $90/ton. Bedding stone and fabric are priced separately by your supplier.
Real-World Delivery Equivalents
Project Inputs
Estimates are approximate and based on typical USDOT/Caltrans/ASTM D6092 gradation reference densities and void ratios. Riprap sizing, layer thickness, and filter design should always be confirmed against a stamped engineering design for slope stability, scour protection, or regulatory compliance this tool is for material quantity planning only.
Most people searching for a riprap calculator need to figure out which class to specify before they can even think about quantity that question comes up more often than the tonnage question itself, so it leads this page.
Riprap is graded by class (commonly labeled R-1 through R-7, or Class I through Class V depending on your state DOT's system), with each class defining a range of stone sizes rather than a single dimension. Smaller classes like Class I handle light erosion control on gentle slopes and ditches. Larger classes like Class IV or V are built for high-flow channels, shoreline protection, and areas exposed to heavy wave or current action. A commonly used engineering rule, D50, refers to the median stone size in the mix half the stones are larger, half are smaller and it's what most state specifications actually reference when they call out a riprap class.
QuickTonnage's Gradation Class selector uses plain-English descriptions instead of just a code number, so you can match your erosion control need to the right class without needing an engineering reference sheet open in another tab.
Class 1 (or R-1) riprap is used for light erosion control small ditches, gentle slopes, and low-flow drainage areas where smaller stone is sufficient to hold soil in place.
Typically $40 to $100+ per ton depending on class size, with larger classes costing more due to sourcing and handling. Installed cost including labor and equipment runs higher.
It depends on your area and the layer thickness required for your gradation class larger stone classes need a thicker layer. QuickTonnage calculates this once you select your class and enter your dimensions.
D50 is the median stone size in a riprap mix the size where half the stones by weight are larger and half are smaller. It's the number most engineering specifications actually reference when calling out a riprap class.
Yes, "riprap," "rip rap rock," and "rip rap stone" all refer to the same erosion-control material. The spacing and phrasing vary by region and habit, not by product.