Rip Rap Calculator
Estimate the rip rap needed to protect shorelines, slopes, and drainage channels from erosion. Enter your area dimensions and stone depth to get tonnage and cost.
Rip Rap Size Classes
Rip rap is classified by stone diameter. Class I (6 to 12 inches) handles low-velocity water and gentle slopes. Class II (12 to 24 inches) protects moderate stream banks and culvert outlets. Class III (24 to 36 inches) resists high-velocity flows and wave action on lakes and reservoirs. Your local stormwater authority or engineer will specify the required class based on site conditions and expected water forces.
Rip Rap Installation Best Practices
Start by grading the slope to a stable angle, typically 2:1 or gentler. Lay non-woven geotextile fabric over the prepared surface, overlapping seams by 12 inches. Place the largest stones at the toe of the slope for stability, then work upward. Avoid dropping stones from height, which can tear the fabric. Fill voids with smaller stones to create a dense, interlocking mat. For shoreline projects, extend the rip rap at least 2 feet below the normal water line to prevent undermining.
Frequently Asked Questions
How thick should rip rap be?
Rip rap thickness depends on water velocity and wave action. Typical residential applications use 12 to 18 inches. High-flow channels may require 24 to 36 inches.
What is the difference between rip rap and crushed stone?
Rip rap consists of large, angular stones (6 to 36 inches) designed to interlock and resist water movement. Crushed stone is smaller and used for bases and drainage.
Do I need geotextile fabric under rip rap?
Yes. A non-woven geotextile fabric should always be placed under rip rap to prevent fine soil from migrating through the stone layer while still allowing water to drain.