Rip Rap Calculator
Construction & Home ImprovementEstimate the minimum recommended rock diameter for rip rap erosion control based on flow velocity, using the Isbash equation.
Minimum Recommended Stone Diameter
Median stone diameter (D50) in inches, from the Isbash equation.
Suggested Layer Thickness
8.25
A commonly cited guideline of 1.5 times the stone diameter.
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Creators
Odeh Ahwal0people find this calculator helpful
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Helpful
Saved
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Construction & Home Improvement calculators
Frequently Asked Questions
What is the Isbash equation?
A widely used preliminary sizing method for rip rap that relates the required stone diameter to the local flow velocity, the specific gravity of the stone, and a turbulence coefficient. It comes from hydraulic engineering references including USACE and FHWA design manuals.
Is this calculator a substitute for a full rip rap design?
No. This is a preliminary estimate. Real revetment or channel protection design should reference a fuller method, such as FHWA HEC-11 or HEC-23, and account for site-specific conditions.
Why does turbulence change the recommended stone size?
Highly turbulent flow exerts more force on individual stones and can dislodge smaller rock more easily, so a conservative design uses a lower turbulence coefficient, which increases the calculated stone size.
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