Riprap Quantity Calculator
Estimate riprap or rock armor quantity from coverage area and thickness. Uses a typical stone unit weight so you can order by the ton or by the yard.
Enter your values, then press Calculate.
How to calculate
Enter the length and width of the armor area and the specified thickness (often 12–24 in). Use 1.4–1.7 tons/yd³ for most dumped riprap unless the spec gives a density. Add waste for over-placement and irregular subgrade.
Formula
Volume (ft³) = length × width × thickness. Cubic yards = ft³ ÷ 27. Tons = cubic yards × tons per cubic yard. Waste multiplies both.
Common use cases
- Channel lining takeoffs
- Outlet protection
- Slope armor
- Checking a quarry quote
Assumptions
- Length × width × thickness is the armor prism, converted to cubic yards.
- Tons use the tons-per-cubic-yard factor you enter (default 1.5 t/yd³ for typical dumped riprap).
- Thickness is the specified layer, often 1.5× D50, not the individual stone size.
- Waste covers placement voids and over-build at the toe.
Limitations
- Does not select D50, class (I/II/III), or a filter layer.
- Does not compute a channel lining design or freeboard.
- 1.5 t/yd³ is a dumped-riprap starting point, not a quarry certificate.
- Does not include geotextile or bedding stone under the armor.
Worked examples
50 × 10 ft at 18 in, 1.5 t/yd³
50 ft × 10 ft × 18 in (1.5 ft) = 27.78 yd³. At 1.5 t/yd³ that is 41.67 tons before waste. Thickness is the specified layer, not D50.
1. Neat volume
50 × 10 × 1.5 = 750 ft³
2. Cubic yards
750 ÷ 27 = 27.7778 yd³
3. Tons
27.7778 × 1.5 t/yd³ = 41.6667 tons
10% waste
1. Neat volume
50 × 10 × 1.5 = 750 ft³
2. Cubic yards
750 ÷ 27 = 27.7778 yd³
3. Tons
27.7778 × 1.5 t/yd³ = 41.6667 tons
Volume first, then a density factor
Riprap is a rectangular prism: length × width × thickness, then ÷ 27 for cubic yards. Tons = yards × tons per cubic yard. 1.5 t/yd³ is a common dumped-riprap field default, not a specification. Heavier stone, grouted riprap, or a quarry ticket will change the tons without changing the geometric yards. Filter fabric, bedding gravel, and grout are separate quantities.
Gradation and waste
The calculator does not know D50 or class (Type 1, 2, etc.). Thickness should match the placed armor thickness on the detail, not the loose stockpile. Waste covers irregular bank, overlapping at keys, and over-placement. Convert tons to truckloads with the truckload estimator after you have loose or ticketed yards, not bank soil yards.
D50 is not the layer thickness
If the spec calls 18 in of Class II riprap, the thickness input is 18 in — the layer — even if D50 is 12 in. Using D50 as thickness under-orders stone. Fifty feet of 10 ft slope at 18 in and 1.5 t/yd³ is 20.83 yd³ and 31.25 tons before waste. Gradation still has to match the spec; this page will not catch an undersized load.
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FAQ
Is 1.5 tons per cubic yard accurate?
It is a common field default for dumped riprap. Use the spec, quarry ticket, or lab density when you have it. Heavier stone or grouted riprap will weigh more.
Does this include filter fabric or bedding?
No. The result is stone volume and tons only. Filter fabric, bedding gravel, and grout are separate quantities.
Is 1.5 tons per cubic yard always right?
It is a common dumped-riprap factor. Dense quarry stone can run higher; some lightweight armor runs lower. Use the quarry factor when you have it.
Do I need the paving-area tool first?
No. Riprap is a volume. Paving area is a wearing-course area without thickness. Enter length, width, and thickness here.
Disclaimer
These calculators are estimating tools for planning and field checks. They are not a substitute for approved plans, specifications, licensed professional engineering, or governing standards. Confirm densities, waste factors, and yields with your supplier and project documents.