Rip Rap Calculator
A rip rap calculator multiplies cubic yards by 1.5 tons per yard: a 30 ft bank, 6 ft up-slope at 12 in deep, needs 10 tons, or 11 with waste, $660 at $60 a ton.
What your order looks like
One bulk delivery is usually easier than hauling it yourself.
6.67 yd³ · 10.0 tons
90 wheelbarrow trips (2 cu ft each)
14 pickup loads (0.75 ton each)
2 small dump truck loads (6 tons each)
Rules of thumb: A wheelbarrow trip is 2 cubic feet of heavy material, about 200 lb, a load most people can push. A pickup load is 0.75 ton, the payload of a full-size half-ton pickup (1,500 lb). A small single-axle dump truck carries about 6 tons.
Rip rap calculator: tons from a bank
A rip rap calculator multiplies bank length, protected width and stone depth to get cubic yards, then multiplies by 1.5 tons per cubic yard. A 30 ft bank protected 6 ft up the slope with a 12 inch layer is 6.67 cubic yards, which weighs 10.00 tons.
Quarries sell rip rap by weight, so the answer is in tons, with a cost at your price per ton.
The formula in plain words
Cubic yards = length × width × (depth in inches ÷ 12) ÷ 27. Tons = cubic yards × 1.5. Cost = tons × price. If the waste box is ticked, tons are multiplied by 1.1 before the cost.
Worked example, a creek bank
A 30 ft section of bank needs protection 6 ft up the slope with 12 inches of stone. Rip rap is $60 a ton.
- Cubic yards: 30 × 6 × 1.0 ÷ 27 = 6.67
- Tons: 6.67 × 1.5 = 10.00
- Cost: 10 × $60 = $600
- With 10% extra: 11.00 tons, or $660
Ask the quarry how many tons its truck carries, so you know whether this is one load or two.
Worked example, a longer bank
A longer stretch of 60 ft, 12 ft up the slope, at 12 inches.
- Cubic yards: 60 × 12 × 1.0 ÷ 27 = 26.67
- Tons: 26.67 × 1.5 = 40.00
- With 10% extra: 44.00 tons, $2,640
If the designer asks for 18 inches on a 30 × 6 ft bank, the order is 15.00 tons instead of 10, and 16.5 tons with the extra.
Tons by bank size at 12 inches
| Length × width | Cubic yards | Tons | With 10% extra |
|---|---|---|---|
| 15 × 3 ft | 1.67 | 2.50 | 2.75 |
| 30 × 6 ft | 6.67 | 10.00 | 11.00 |
| 30 × 10 ft | 11.11 | 16.67 | 18.33 |
| 60 × 12 ft | 26.67 | 40.00 | 44.00 |
How to measure the bank
- Walk the bank and measure its length along the water edge.
- Measure the width up the slope, along the surface, from the toe of the bank to the top of the area you are armoring. This number is longer than the horizontal distance.
- Find the high water mark, since the stone has to reach above the flood line.
- Use the placed depth, not a compacted one. Rip rap is placed, not compacted like base stone.
- Divide a bank that changes slope into sections and calculate each one.
Common mistakes
- Measuring the horizontal distance instead of the distance along the slope. That undercounts a steep bank.
- Leaving out the toe. The bottom of the armor is often dug in below the stream bed, which needs extra stone.
- Skipping the fabric. Without it, fine soil washes out and the stone sinks.
- Choosing stone size by guess. Fast water moves small stone.
- Working in a stream without checking permits. Many areas need approval for work along waterways.
Delivery and placement
Ten tons is 20,000 pounds, and individual stones can be too heavy to lift by hand. Plan to place the stone with a machine such as a skid steer or a small excavator, and tell the supplier where the truck can dump. Small rip rap can be hand placed, but large stones need equipment.
Place the stone in a layer of the thickness you ordered, with the larger pieces locked together and the gaps filled by smaller ones. Do not tip it down the bank and walk away, because loose, thin spots wash out first. The toe, which is the bottom edge at the water, should be dug in so the stone does not slide. Mark the finished depth with stakes so you can check it as you go.
Related pages
Ballast and other large stone have their own page in the ballast calculator. Behind the rip rap, drainage stone is sized with the drain rock calculator, and the slope calculator helps you convert grade to angle.
Frequently asked questions
What do I enter for length and width?
Length is how far along the bank you are protecting. Width is how far up the slope the stone goes, measured along the slope surface from the water edge to the top of the armor. Depth is the thickness of the stone layer.
Why is rip rap heavier than other gravel?
It is large, dense rock such as granite or limestone, and the calculator uses 1.5 tons per cubic yard. Actual weight changes with rock type and stone size, so confirm the figure with your quarry.
What size stone counts as rip rap?
Rip rap is graded by stone size, usually in a range of inches or by weight class. Which class you need depends on water velocity and slope. A civil engineer or the local public works office can specify it.
Do I need fabric or bedding under it?
Often yes. A geotextile filter fabric or a layer of smaller stone under the rip rap keeps the soil from washing out through the gaps. This is part of a good design, and it adds material that this calculator does not count.
What depth should I order?
Depth comes from the design for your bank and is tied to the stone size. The 12 inch example suits smaller stone on a gentle bank. Ask the designer or supplier for the right depth.
Should I add waste?
Yes. Tick the 10% box. Stone settles into the voids and bedding, and an uneven bank takes more than a straight calculation. On the 30 ft example it moves the order from 10 to 11 tons.
Estimates only. Verify quantities with your supplier before purchasing.