Rip Rap Calculator
Find how many tons of rip rap stone you need. The layer must be thick enough for the stone size.
Measure your project
Your answer
That is 4.89 cubic yards. We added 10% extra.
For a bank, shore or ditch, check your local building rules or ask a builder or engineer.
What it costs
Rip rap: $79 a ton, the middle of 5 US sellers (Oct 2026), before delivery.
Quick answers
- Tons in a yard
- We use 1.65 tons. A South Carolina yard says 1.35, and Tennessee DOT 1.75.
- Layer thickness
- No thinner than the largest stone or 12 in, by FHWA's rule. Add 50% under water.
- What a ton covers
- 16.4 sq ft for each ton, at 12 in thick.
- Price
- About $79 a ton, from only 5 sellers. Treat it as rough.
How to work it out
- Measure the length and width of the bank, shore or ditch in feet.
- Pick the layer thickness in inches. Multiply it by the square feet, then divide by 324 for cubic yards.
- Tons of rip rap = cubic yards × 1.65.
20 × 6 × 12 ÷ 324 = 4.44 cubic yards
4.44 × 1.65 = 7.33 tons
FHWA rip rap classes
"Class" means different things to different agencies. So when a yard quotes a class, ask whose it is.
FHWA, the federal road agency, sorts rip rap into 10 classes, I to X. Each class is set by the size of its middle stone. Here are the 4 smallest.
| Class | Middle stone | Largest stone | Middle stone weighs | Layer | Layer under water |
|---|---|---|---|---|---|
| Class I | 6 in | 12 in | 20 lb | 12 in | 18 in |
| Class II | 9 in | 18 in | 60 lb | 18 in | 27 in |
| Class III | 12 in | 24 in | 150 lb | 24 in | 36 in |
| Class IV | 15 in | 30 in | 300 lb | 30 in | 45 in |
Stone sizes are FHWA's middle and top sizes. Layers are worked out from FHWA's rule.
FHWA's rule takes the biggest of three numbers. They are the largest stone's size, 1.5 times the middle stone's size, and 12 in.
Under water, make the layer 50% thicker.
State classes: North Carolina and Virginia
States use their own classes. North Carolina sorts rip rap by stone size, and Virginia by stone weight.
| Class | Stone sizes | Layer, NC rule |
|---|---|---|
| Class A | 2–6 in | 9 in |
| Class B | 5–12 in | 18 in |
| Class 1 | 5–17 in | 25.5 in |
| Class 2 | 9–23 in | 34.5 in |
NC rule, from a 2025 draft manual: at least 1.5 times the largest stone, and never under 6 in.
| Class | Each stone weighs |
|---|---|
| Class AI | 25–75 lb |
| Class I | 50–150 lb |
| Class II | 150–500 lb |
| Class III | 500–1,500 lb |
From a Hampton Roads standard that follows VDOT.
A yard's own label can differ again. Palmetto Sand & Gravel, in South Carolina, sells 5–10 in stone as Class A. It suggests a 12 in layer to start.
Why a ton covers more or less
Rip rap weights disagree, and that changes how far a ton goes. Here is each figure at a 12 in layer.
| Whose weight | Tons a yard | One ton covers |
|---|---|---|
| Palmetto, a South Carolina yard | 1.35 | 20 sq ft |
| Front Range, a Colorado yard (ours) | 1.65 | 16.4 sq ft |
| Tennessee DOT | 1.75 | 15.4 sq ft |
We use 1.65 tons. It is the higher of the two yard figures, so your order is less likely to fall short.
Before you order
- Ask the yard about bedding stone or filter fabric to go underneath.
- Ask the yard for the class and the stone sizes in inches.
- Ask if the price is per ton, and what delivery costs.
Fabric is not in our tons. We found no figure for how much fabric to overlap.
Prices are thin. Counting all 7 rip rap items we found, the middle was $90 a ton.
This page helps you count stone, not design a bank. For the design, check your local building rules or ask a builder or engineer.
Questions people ask
How much rip rap do I need?
Measure the area and pick a layer thickness for your stone size. For a 20 × 6 ft bank, 12 in thick, that comes to about 7.3 tons. With 10% extra, order about 8.1.
How do you calculate rip rap tonnage?
Square feet times layer thickness in inches, divided by 324, is the cubic yards. Multiply that by 1.65 for tons.
How much does 1 ton of rip rap cover?
At 12 in thick, a ton covers about 16.4 sq ft. Make it 18 in thick and a ton covers about 10.9 sq ft.
How much rip rap is in a ton?
About 0.61 cubic yards, or 16.4 cubic feet, at 1.65 tons a yard.
How thick should rip rap be?
FHWA takes the most of three: the largest stone's size, 1.5 times the middle size, or 12 in. North Carolina's 2025 draft manual says 1.5 times the largest stone, and 6 in or more.
What is Class A rip rap?
It depends on who says it. NCDOT Class A is 2–6 in stone. A South Carolina yard sells 5–10 in stone as Class A.
Do I need fabric under rip rap?
FHWA says to set rip rap on bedding stone, filter fabric or both. A bed of stone should be at least 6 in thick.
How much does rip rap cost?
About $79 a ton, one price per seller from 5 sellers. They ran $75–$125, so treat it as rough.
Where our numbers come from
- Rip rap classes and thickness: FHWA HEC-23
- Rip rap classes: NCDOT Table 1042-1
- Rip rap thickness: NC DEQ erosion control manual 6.15
- Rip rap classes by stone weight: Virginia regional standard 414
- Coverage and weights: Front Range Material conversion sheet
- Rip rap weight: Tennessee DOT structures guide (1.75 tons per cubic yard)
- Rip rap layer and extra: Palmetto Sand & Gravel
- Rip rap price: the middle of 5 US sellers (Oct 2026; few prices)
Made by BuildersCount. Last checked 3 Oct 2026.
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