Water moving across bare soil carries that soil with it, and on a slope or a bank it does so fast. Rip rap is large, angular rock placed in a layer to armor the ground against that moving water, so the stone takes the force instead of the soil. The job sets the stone size: light landscape runoff needs small rip rap, while slopes, channels, and shorelines need progressively larger stone to stay put. Here is how to pick a size and install it so it holds.
What rip rap is
Rip rap is broken quarry stone with rough, angular faces, sized larger than ordinary decorative gravel. The angles matter. When the pieces are graded into a layer, the irregular faces interlock and wedge against each other, so the blanket of stone resists being lifted or rolled by flowing water. Rounded river rock does not hold as well, because smooth stones slide past each other and wash out.
You will see rip rap along ditches and culvert outlets, at the toe of slopes and embankments, and on pond and shoreline banks. In a yard it shows up wherever a downspout, swale, or graded slope sends concentrated water across the ground and a planting or mulch would just erode away.
Sizing rip rap by the job
Rip rap is sorted roughly by stone diameter, and the size you want climbs with the force of the water and the steepness of the grade. Bigger, faster water needs bigger stone so individual pieces are too heavy to move. The table below matches a size range to a typical use. Treat it as a starting point, not an engineering spec.
| Approximate stone size | Typical use |
|---|---|
| Small, roughly 3 to 6 inches | Light landscape runoff, downspout splash areas, gentle swales, small dry beds |
| Medium, roughly 6 to 12 inches | Slopes and embankments, ditch and channel linings, culvert aprons |
| Large, roughly 12 inches and up | Shorelines, stream banks, high-flow channels, heavy erosion exposure |
The faster the water and the steeper the bank, the larger the stone you want. A backyard downspout that pools after a storm is a small rip rap problem. A graded slope shedding runoff is a medium one. A pond edge taking wave action or a channel that runs hard in heavy rain is where the large stone earns its place. For serious channels, shorelines, or anything carrying real flow, have the design checked against your local guidelines, since the right size there is a calculation, not a guess.
If your need is closer to a wall face or a structural edge than armoring against flow, larger wall stone may suit it better. Our wall rock collection covers that range. For a broader look at how rock handles water in the yard, see our guide to landscape rock for drainage and erosion control.
Install basics
Rip rap works as a system, not just a pile of rock. A few fundamentals make the difference between a layer that holds for years and one that slips or undercuts.
- Lay it over filter fabric. Put a geotextile filter fabric down on the graded soil first. The fabric lets water pass while holding the underlying soil in place, so water cannot wash the dirt out from beneath the stone and collapse the layer.
- Key in the toe. The bottom edge, the toe, is where failure starts. Dig a shallow trench at the base and set the first course of stone into it so the layer is anchored. Without a keyed-in toe, water gets under the lowest stones and unravels the whole blanket from the bottom up.
- Give it enough depth. A single scatter of stones is not armor. The layer needs enough thickness that the pieces interlock and there are no gaps down to the soil. As a rule of thumb the layer is at least as thick as the largest stones, and often thicker. Bigger stone means a deeper layer.
- Grade and place, do not just dump. Smooth the slope first, then place the stone so faces wedge together and the surface is reasonably even, with smaller pieces filling the voids between larger ones.
Done this way, the fabric holds the soil, the toe holds the bottom, and the interlocked depth holds the surface against the water.
Ordering and delivery
Rip rap is heavy. Because the stone is large and a typical job covers real area at real depth, orders add up in weight quickly, and large or distant deliveries ship by freight rather than standard parcel. Local orders can be delivered or picked up at one of our two California yards. For anything beyond a small quantity, tell us your stone size, square footage, and delivery ZIP and let us price it: request a quote. Rates vary by distance and weight, so a quote is more honest than a flat number.
You can also check your area and an estimated delivery on our delivery zone map and ZIP checker before you order. When you are ready for the stone, browse our rip rap collection.
Frequently asked questions
What is rip rap used for?
Rip rap is large angular rock placed in a layer to protect soil from moving water. It is used on slopes and embankments, along ditches and channels, at culvert outlets, and on pond and shoreline banks, anywhere flowing water would otherwise erode the ground.
What size rip rap do I need?
It depends on the job. Light landscape runoff and downspout areas use small rip rap of roughly 3 to 6 inches. Slopes and channel linings use medium stone of roughly 6 to 12 inches. Shorelines and high flow use large stone of 12 inches and up. The faster the water and steeper the grade, the larger the stone.
Do I need filter fabric under rip rap?
Yes, in almost every case. A geotextile filter fabric under the stone lets water pass while keeping the soil from washing out beneath the layer. Without it, water can scour the dirt out from under the rock and cause the blanket to slump or fail.
How thick should a rip rap layer be?
Thick enough that the stones interlock with no gaps down to the soil. A common rule of thumb is a layer at least as thick as the largest stones, and often thicker for bigger stone or heavier flow. A single scatter of rock is not armor.
How is rip rap delivered?
Because it is heavy and large orders add up in weight, rip rap ships by freight for large or distant orders, or you can pick it up at one of our California yards. Tell us your stone size, area, and ZIP and request a quote, since rates vary by distance and weight.
Get the materials
Browse our rip rap collection for erosion control, or wall rock for heavier structural edges. For large or far orders, request a quote and check coverage and timing on our delivery zone map. We deliver nationwide from our California yards.