Rip Rap Calculator

Estimate rip rap stone for bank stabilization, channels, and shorelines. Pick a rock class to load a typical layer thickness and density, or enter your project spec directly, and get tons for your coverage area.

Rip Rap Details

Rock Class

Length

Width

Layer Thickness (auto-filled)

Density (auto-filled)

tons/yd³

Pick a rock class and enter your coverage area to see tons needed.

The formula

Tons = (Length ft × Width ft × Layer Thickness in ÷ 12) ÷ 27 × Density (tons/yd³)

Layer thickness scales with rock class — bigger stone needs a thicker layer to interlock. The presets pair each class with a typical layer (Class I ≈ 9 in up to Class IV ≈ 24 in) and density; DOT and project specs override these, so use spec values when you have them.

Placement notes

Rip rap goes over a geotextile filter fabric or granular filter layer so the soil underneath can’t wash out through the voids. Measure your area along the slope face, not the horizontal footprint — a 2:1 slope face is about 12% longer than its plan-view width.

Frequently Asked Questions

What do rip rap classes mean?

Classes group stone by size: higher classes are larger rock for higher flow velocities and wave energy, placed in proportionally thicker layers. Exact size ranges vary by state DOT.

How thick should a rip rap layer be?

A common rule is 1.5–2× the median stone size, which is where the class presets (9–24 inches) come from. Follow the project spec when one exists.

Do I need fabric under rip rap?

Almost always yes — geotextile filter fabric (or a granular filter) prevents the underlying soil from piping out through the stone voids and undermining the layer.