Rip Rap Calculator
Tons, cubic yards, and coverage for channel lining, slope protection, and bank stabilization. Pick a class, enter the area you’re armoring, and add a depth. The calculator returns tonnage and cubic yards based on bulk in-place density. Imperial and metric.
Results
Estimates only. Coverage assumes bulk in-place density of 110 lb/ft³ (1,762 kg/m³). That figure is what installed rip rap weighs after the typical 30 to 35% void space settles in, not the solid rock material density. Solid rock material runs 150 to 175 lb/ft³ per USACE EM 1110-2-1601 and NRCS Construction Spec 461; the 110 figure is the bulk delivery weight your supplier will quote. Actual delivered tonnage varies 1.4 to 1.7 tons per cubic yard depending on stone size, gradation, and placement method. Confirm minimum delivery quantities and bulk pricing with your supplier before ordering.
How to use this calculator
Start with the application. The Channel lining preset assumes 12 inch depth and suits ditches and small swales. Slope protection runs 18 inches and covers most graded embankments. Bank stabilization is 24 inches for active erosion zones along streams or ponds. Bridge abutment is 36 inches for permanent armoring around piers, abutments, and spillway aprons. Custom skips the preset if you already know the depth.
Pick a class next. The class sets the median stone size for reference and matches what suppliers and DOT specs use to quote rip rap. Class 1 stones average 9 inches, Class 2 average 15 inches, Class 3 average 21 inches, and Class 4 average 27 inches. Pair the class to the application using the reference table below if you’re not sure which fits.
Enter the shape and dimensions of the area you’re armoring. For a rectangular channel, that’s length × width along the run. For a circular basin or culvert outlet, enter the diameter. For irregular shapes, enter the surface area directly under custom area.
Add a waste percentage. 10 to 15% covers most jobs. Steep slopes, irregular subgrades, and projects with strict gradation specs run higher.
The result rows return cubic yards, tons, half cubic foot bags, and coverage area. Bulk delivery by the ton is the standard channel for any rip rap project larger than a small decorative bed; the bag row is shown for parity with the other gravel calculators.
Understanding the math
Rip rap volume math follows the same pattern as the rest of the gravel family. Multiply the surface area by the depth to get cubic feet of installed rip rap. Multiply by 110 lb/ft³ (1,762 kg/m³) to get pounds, then divide by 2,000 to get tons. The waste percentage scales the base volume up to cover undersize fill, oversize rejects, and placement loss. The 110 figure is bulk in-place density with typical 30 to 35% void space, not solid rock material; suppliers commonly quote 1.4 to 1.7 tons per cubic yard depending on gradation.
volume_ft3 = area_ft2 × depth_ft weight_lbs = volume_ft3 × 110 weight_tons = weight_lbs / 2000 volume_yd3 = volume_ft3 / 27
Worked example. A slope protection installation 30 ft by 20 ft at 18 inch depth with 12% waste. Surface area is 30 × 20 = 600 sq ft. Depth in feet is 18 / 12 = 1.5 ft. Volume is 600 × 1.5 = 900 cubic feet. Weight is 900 × 110 = 99,000 lbs, which is 49.5 tons. With 12% waste added, you need about 55.4 tons (50.3 tonnes in metric).
Rip rap classes and coverage
Coverage values computed at the locked density of 110 lb/ft³. Each row pairs a class to an application typical for that stone size. Row 2 is below the 2 × D50 structural rule and reflects decorative use only.
| Class | Use Case | Recommended Depth | Coverage per Ton |
|---|---|---|---|
| Class 1 (D50 9 in) | Channel lining, light slope | 12 in | 18 sq ft |
| Class 1 (D50 9 in) | Decorative water feature edges | 9 in | 24 sq ft |
| Class 2 (D50 15 in) | Slope protection, bank revetment | 18 in | 12 sq ft |
| Class 3 (D50 21 in) | Bank stabilization, heavy slope | 24 in | 9 sq ft |
| Class 4 (D50 27 in) | Bridge abutment, spillway | 36 in | 6 sq ft |
| Class 4 (D50 27 in) | Submerged abutment (+50% thickness) | 54 in | 4 sq ft |
Frequently asked questions
How do I figure how much rip rap I need?
Multiply the surface area by the depth to get cubic feet of rip rap. Divide by 27 to get cubic yards, or multiply by 110 lb/ft³ and divide by 2,000 to get tons. Add 10 to 15% for waste. The class you select sets the median stone size (D50), and the application preset sets a recommended depth: 12 inches for channel lining, 18 inches for slope protection, 24 inches for bank stabilization, 36 inches for bridge abutments. Bulk delivery by the ton is the standard channel for any rip rap project beyond a small decorative bed.
How much area does 1 ton of riprap cover?
Coverage depends on depth. At 110 lb/ft³ bulk density, 1 ton equals about 18.18 cubic feet of installed rip rap. Divide by the depth in feet to get coverage in square feet. At 12 inch depth, 1 ton covers about 18 sq ft. At 18 inch depth, about 12 sq ft. At 24 inch depth, about 9 sq ft. At 36 inch depth, about 6 sq ft. The reference table above breaks this down by class and application.
How much does a cubic yard of Class 2 riprap weigh?
About 1.49 tons. The math is 1 cubic yard × 27 ft³/yd³ × 110 lb/ft³ ÷ 2,000 lb/ton. Class doesn't change the bulk density much in practice; the variance comes from in-place void space, which runs 30 to 35% for typical rip rap gradations. Suppliers commonly quote 1.4 to 1.7 tons per cubic yard depending on the specific gradation, the source quarry, and how the stone settles after placement. Class 2 sits in the middle of that range.
How much is 15 tons of rip rap?
In coverage terms, depth determines how far 15 tons goes. At 12 inch depth (Class 1, channel lining), 15 tons covers about 270 sq ft. At 18 inch depth (Class 2, slope protection), about 180 sq ft. At 24 inch depth (Class 3, bank stabilization), about 135 sq ft. At 36 inch depth (Class 4, bridge abutment), about 90 sq ft. For a price estimate, enter your supplier's delivered cost in the optional price per ton field. Rip rap pricing varies widely by region, gradation, and haul distance, so this calculator doesn't ship with a default.
What size rip rap do I need?
Match the class to the application using the median stone size (D50). Class 1 (D50 ≈ 9 inches) suits decorative beds, light channel lining, and small drainage. Class 2 (D50 ≈ 15 inches) is the most common pick for slope protection on graded embankments. Class 3 (D50 ≈ 21 inches) handles active bank stabilization on streams and ponds. Class 4 (D50 ≈ 27 inches) is for bridge abutments, spillway aprons, and permanent armoring on high-velocity channels.
For permanent flood control work, USACE and FHWA specs size rip rap to handle the design flow velocity, with stone size tied to a hydraulic calculation rather than picked from a table. The class system used here reflects the gradation tiers that suppliers and most state DOTs use for ordering, which is what you need at the takeoff stage.
Can I use this calculator with metric measurements?
Yes. Toggle the unit system at the top of the form. Inputs flip to meters, centimeters, and tonnes. The math runs in metric source-of-truth using 1,762 kg/m³ as the locked bulk density (the metric equivalent of 110 lb/ft³). Result rows display cubic meters, tonnes, and square meters of coverage. The reference table flips with the unit toggle to show metric coverage per tonne.
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