Rip Rap Calculator
Calculate rip rap accurately for your build. Get material quantities, waste allowances, and project cost breakdowns. Free to use with no signup required.
Formula
Tons = (L x W x Thickness/12) / 27 x Density
Multiply the area length (ft) by width (ft) by thickness (converted from inches to feet) to get volume in cubic feet. Divide by 27 to convert to cubic yards. Multiply by the rip rap density (typically 1.3 to 1.5 tons per cubic yard depending on stone class) to get total tonnage needed.
Worked Examples
Example 1: Stream Bank Stabilization
Problem: Calculate rip rap for 100 ft of stream bank, 8 ft slope width, Class II stone at 18\" thick.
Solution: Area = 100 x 8 = 800 sq ft\nThickness = 18 / 12 = 1.5 ft\nVolume = 800 x 1.5 = 1,200 cu ft = 44.44 cu yd\nTons = 44.44 x 1.40 = 62.22 tons\nTruck loads = ceil(62.22 / 20) = 4
Result: 44.44 cu yd, 62.22 tons, 4 truck loads
Example 2: Culvert Outlet Apron
Problem: Calculate Class III rip rap for a 20 ft x 15 ft outlet apron at 24\" thick.
Solution: Area = 20 x 15 = 300 sq ft\nThickness = 24 / 12 = 2 ft\nVolume = 300 x 2 = 600 cu ft = 22.22 cu yd\nTons = 22.22 x 1.45 = 32.22 tons
Result: 22.22 cu yd, 32.22 tons, 2 truck loads
Frequently Asked Questions
What is rip rap and when is it used?
Rip rap (also spelled riprap) is loose angular stone placed along shorelines, stream banks, bridge abutments, and slopes to protect against erosion caused by water flow and wave action. Stones typically range from 4 inches to 36 inches in diameter depending on the class and application. Rip rap works by absorbing and dissipating wave energy, slowing water velocity, and armoring the soil underneath. It is one of the most commonly used erosion control methods in civil engineering because of its effectiveness, relatively low cost, natural appearance, and ability to conform to irregular surfaces.
How thick should a rip rap layer be?
Rip rap thickness depends on the stone class and design velocity of the water. A general rule is that the blanket thickness should be at least 1.5 times the maximum stone diameter, or a minimum of 12 inches, whichever is greater. For Class I stone (4 to 8 inches), typical thickness is 12 to 18 inches. Class II (8 to 15 inches) usually requires 18 to 24 inches. Class III and IV for high-velocity channels may need 24 to 36 inches or more. Corps of Engineers and state DOT specifications provide detailed design charts based on flow velocity and bank slope.
Do I need filter fabric under rip rap?
Yes, a geotextile filter fabric is almost always recommended under rip rap. The fabric prevents fine soil particles from migrating through the stone layer, which would cause the rip rap to settle into the soil and lose effectiveness. Without filter fabric, piping and undermining can occur, leading to failure of the erosion protection. Non-woven geotextile fabric with a minimum weight of 8 oz per square yard is standard for most applications. Some designs use a graded stone filter layer instead of fabric, but this requires more material and careful gradation control.
How much does rip rap cost per ton?
Rip rap prices typically range from $25 to $75 per ton depending on the stone class, source distance, and regional availability. Class I and II smaller stone averages $30 to $45 per ton, while larger Class III and IV stone runs $45 to $75 per ton due to the difficulty of quarrying and handling. Delivery costs for rip rap are significant because of its weight, typically adding $8 to $15 per ton for deliveries within 20 miles. Installation labor for machine-placed rip rap adds $15 to $30 per ton. Total installed costs commonly range from $50 to $120 per ton.
How do I interpret the result?
Results are displayed with a label and unit to help you understand the output. Many calculators include a short explanation or classification below the result (for example, a BMI category or risk level). Refer to the worked examples section on this page for real-world context.
Is Rip Rap Calculator free to use?
Yes, completely free with no sign-up required. All calculators on NovaCalculator are free to use without registration, subscription, or payment.