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Rip rap calculator for Mississippi

Work out shoreline and slope tonnage using an armor-layer depth, not a shallow landscaping depth.

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Enter a depth between 0.25 and 24 inches

A ton of riprap covers about 17 square feet. It sounds low, but it is correct. Armor stone is placed in layers 12 inches thick or more, leaving each ton to cover about a tenth of the area landscape rock would. The pile may look modest beside the bank it needs to protect. This calculator bases its result on layer depth, using 3,100 lb per cubic yard for stone generally sized 4 to 12 inches and up.

How to measure a protected bank

  1. Take the measurement down the slope face itself instead of across level ground, then multiply it by the shoreline or channel length.
  2. Use a layer 1.5 to 2 times the largest stone dimension, with 12 inches as the practical minimum for erosion control.
  3. Divide cubic feet by 27 for cubic yards, then multiply by 1.55 for tons.
Tons = (Slope-face area sq ft × Layer thickness in ÷ 12) ÷ 27 × 1.55

Tons of coverage

Layer thickness1 ton coversTons per 100 sq ft
12 inches≈ 17 sq ft5.7
18 inches≈ 12 sq ft8.6
24 inches≈ 9 sq ft11.5

Steps for stone that stays in place

  • Put fabric or bedding below the stone: use non-woven geotextile beneath it, or 3-4 inches of #4 stone. Rock set straight on bare soil can look good for a season, then settle when the bank below it washes away.
  • Start by anchoring the toe. Set the lowest stones below the waterline or expected scour depth, since erosion can unravel riprap from underneath.
  • Before placing stone, cut the slope back to 2:1 or flatter. A face any steeper needs engineering, not simply additional rock.
  • Machine-set or hand-place the exposed top course so the stones lock together rather than staying where they happen to land.
  • Extend the apron 4-6 pipe diameters beyond culvert outlets. That downstream area takes the force of the discharge.

Example: 50 feet of pond bank

A shoreline slope 6-foot high and 50 feet long covers 300 square feet. For an 18-inch layer: 300 x 1.5 = 450 cubic feet = 16.7 cubic yards, about 26 tons of riprap, 27 with the small allowance. Use a roll of geotextile, or about 4 tons of #4 stone for rock bedding. Check the delivery route before you order. The last 20 feet by a pond edge can bog down loaded trucks, and relocating stone costs twice.

Once the first heavy storm passes

After the water recedes, take a walk along the bank. Check for rock that has moved near the toe, exposed soil between stones, or fabric showing through. Put shifted pieces back, use reserve stone to fill sparse areas, and inspect the outfall apron for erosion. Spending Ten minutes on this check twice yearly keeps maintenance simple: riprap handles the protection work without much from you.

A quick look at size classes

Size the stone for the force of the water. Four to eight inch riprap is suited to pond banks, downspout outfalls, and slow streams. Use eight to twelve for lake edges exposed to boat wake and faster channels. Highway and spillway work is engineered with its own stone classes and layer thicknesses, so use the drawing rather than this page. When choosing between sizes, go larger and increase the layer thickness. Heavier rock allows more margin.

Riprap amounts, sizing, and installation

How can I calculate the rip rap I need?
Take the slope-face area, multiply it by layer thickness in feet, then divide by 27 and multiply by 1.55. For a 10 x 10 sample area at 12 inches deep, the result is 37 cubic feet, or roughly 2.1 tons.
How much coverage comes from 1 ton of riprap?
At a 12-inch depth, plan on roughly 17 square feet per ton; at 18 inches, plan on 12. For budget planning, use 5.5 to 6 tons for every 100 square feet at the normal layer depth.
What does a 1 ton pile of rip rap look like?
Picture a pile equal to two parts of a cubic yard split into three: about the volume of a washing machine, with 25-35 stones in the 6-8 inch range. It can look modest in a pile, but at the right thickness it spreads across a 4 x 4 section of bank.
What is the cost of 1 ton of rip rap?
RipRap costs more than construction stone and is sold by size class. The current amount appears on our RipRap product page, and delivery is free. Fabric and bedding stone add a fraction more, and getting those parts right costs the least within the system.
What layer depth does rip rap need?
Make the rock layer one and a half to two times the largest stone size, with 12 inches as the minimum. Standard 4-12 inch residential rock generally needs 12-18 inches, while larger material or swift water calls for 24.
Is hand placement possible for rip rap?
For stone up to about 6-8 inch, hand placement can work with work gloves and plenty of strength, though a ton still means 25-35 lifts. Use a machine for larger rock. A skid steer can do in an hour what takes a crew a day to place by hand.
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Protect exposed banks with stone.

Order RipRap by the ton with delivery at no charge, and place #4 bedding stone beneath it.

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