Riprap calculator: how many tons of riprap do I need?
35 tons
20.00 cubic yards, 18 in thick, of 2 in to 1.25 ft stone (Class A-1) · 1.75 tons per cubic yard (TDOT) · for 30 × 12 ft, Class A-1
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3/8 or 10' 6".
35 tons
20.00 cubic yards, 18 in thick, of 2 in to 1.25 ft stone (Class A-1) · 1.75 tons per cubic yard (TDOT)
Source: Tennessee DOT Standard Specifications 2021, 709.03 riprap classes, and Roadway Design Guidelines 4-709.05, read October 26, 2026. Data sheet (PDF)
Covering 30 × 12 ft with TDOT Class A-1 riprap, a 1.5 ft layer of 2 in to 1.25 ft stone, takes 20 cubic yards: 35 tons at the 1.75 tons per cubic yard Tennessee DOT uses for estimates.
A worked example
A culvert outlet apron 47 ft long and 9 1/2 ft wide in Class B riprap needs 72.3 tons. 446.5 sq ft in a 2.5 ft layer is 1,116.25 cu ft, 41.34 cubic yards; × 1.75 = 72.3 tons. The same apron in Class A-1 would be 43.4 tons.
How many tons of riprap per square foot?
At TDOT's 1.75 tons per cubic yard, 100 sq ft takes 9.72 tons of Class A-1 or A-2 in its 1.5 ft layer, 16.2 tons of Class B at 2.5 ft and 22.7 tons of Class C at 3.5 ft: about 0.1, 0.16 and 0.23 tons per square foot.
How thick is a riprap layer?
TDOT 709.03 sets 1.5 ft for Class A-1, with a 3 in tolerance, 2.5 ft for Class B, within 4 in, and 3.5 ft for Class C, within 6 in. The layer is a little thicker than the largest stone of its class: 1.25, 2.25 and 3 ft.
What else it is called
Also written rip rap or rip-rap, and searched as a riprap calculator in tons, rip rap calculator square feet or riprap volume calculator. TDOT measures machined riprap by the ton or by the cubic yard in place (709.11).
Tons per 100 sq ft by class
| Class | Stone size | Layer | Cubic yards per 100 sq ft | Tons per 100 sq ft |
|---|---|---|---|---|
| Class A-1 | 2 in to 1.25 ft | 18 in | 5.56 | 9.72 |
| Class A-2 | 2 in to 1.25 ft | 18 in | 5.56 | 9.72 |
| Class A-3 | 2 to 6 in | 8 in (from the plans) | 2.47 | 4.32 |
| Class B | 3 in to 2.25 ft | 30 in | 9.26 | 16.2 |
| Class C | 5 in to 3 ft | 42 in | 13 | 22.7 |
TDOT Standard Specifications 2021, 709.03: Class A-1 and A-2 in a 1.5 ft layer, B in 2.5 ft and C in 3.5 ft; Class A-3 takes the thickness on the plans, 8 in (0.67 ft) in TDOT's own bridge apron example. Tons at 1.75 per cubic yard, TDOT Roadway Design Guidelines 4-709.05.
Where the numbers come from
- Classes and layers: Tennessee Department of Transportation, Standard Specifications for Road and Bridge Construction (January 1, 2021), 709.03. Machined riprap Class A-1 varies from 2 inches to 1.25 feet in a 1.5 foot layer; A-2 is identical, or 1 foot of hand-placed rubble stone instead; A-3 from 2 to 6 inches in the thickness shown on the plans; Class B from 3 inches to 2.25 feet in 2.5 feet; Class C from 5 inches to 3 feet in 3.5 feet. Read October 26, 2026. TDOT Standard Specifications 2021 (PDF)
- Tons: TDOT Roadway Design Guidelines, 4-709.05, «For estimating purposes, multiply cubic yards by 1.75 to convert to tons». TDOT's Structures Calculation Guide works it on a bridge apron: 2,914 sq ft of Class A-1 at 1.50 ft is 162 cubic yards and 283 tons. TDOT Roadway Design Guidelines, section IV (PDF)
- The rest is arithmetic: cubic yards = length × width × layer in feet ÷ 27; tons = cubic yards × 1.75.
The classes and the 1.75 factor are Tennessee DOT's; other state DOTs grade riprap with their own classes. The page works out the quantity for a class, not which class a channel needs: that comes from the flow velocity in a hydraulic design.
By Javier Miralles · Last updated . How this site is made.
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