Riprap Calculator
A 30 ft by 8 ft bank at 18 inches is 13.33 cubic yards and 17.42 short tons at 1,550 kg/m³.
Last updated . 1,550 kg/m³ and 2,610 lb per cubic yard are the loose riprap pair in the FHWA Federal Lands earthwork exhibit. This page’s conversion of 1,550 prints 2612.61 lb and 1.31 short tons. The 2.61 lb gap is rounding.
Decorative stone is the landscape rock calculator. Large open-graded base stone is No. 2, not riprap.
Riprap layer
FHWA Federal Lands loose riprap: 1,550 kg/m³. The same row lists 2,610 lb/yd³. This tool displays 2612.61 lb because of unit rounding.
Volume and weight
Finished cubic yards
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Order cubic yards
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Order short tons
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Order tonnes
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Class names, not a copied table
Riprap class is the stone size. Thickness of the blanket is a separate number, and 18 inches in the example is a thickness. Mile High Flood District classes by median stone size are very light 6 inch, light 9 inch, medium 12 inch, heavy 18 inch, and very heavy 24 inch. That specification also wants specific gravity of at least 2.5 and bulk density of at least 1.3 ton per cubic yard. NHDOT 583, following FHWA HEC-23, uses nominal width: Class I 6 inch, Class III 12 inch, Class V 18 inch, Class VII 24 inch, Class IX 36 inch. The percent-by-volume tables in those specs are not reprinted here.
| A class name you will see | About |
|---|---|
| MHFD VL / NHDOT Class I | 6 in rock |
| MHFD L | 9 in d50 |
| MHFD M / NHDOT Class III | 12 in rock |
| MHFD H / NHDOT Class V | 18 in rock |
| MHFD VH / NHDOT Class VII | 24 in rock |
| NHDOT Class IX | 36 in nominal width |
The 1,550 kg/m³ figure
Source: FHWA Federal Lands Highway, Project Development and Design Manual exhibit for earthwork, riprap rock loose, 1,550 kg/m³ and 2,610 lb/yd³ (highways.dot.gov earthwork design). At this site’s factors, 1,550 kg/m³ is 1.31 short tons and 2612.61 lb per cubic yard. Use 2612.61 when you are reading this calculator. The FHWA pair is the source, and the 2.61 lb difference is stated so the two are not treated as a mismatch in the rock.
Coverage
One cubic yard covers 18 square feet at 18 inches and 27 square feet at 12 inches. A 30 by 8 foot bank is 240 square feet. At 18 inches that is 13.33 cubic yards. No compaction allowance is added. Voids are already part of the loose density.
Worked example
Leave length at 30 ft, width at 8 ft, depth at 18 in, and density at 1550. Finished and order cubic yards both read 13.33. Order short tons read 17.42. Order tonnes read 15.80. The formula line shows 360.00 ft³, 10.19 m³, allowance 0.00 percent, and 17.42 short tons at 1550 kg/m³.
Frequently asked questions
How much does a yard of riprap weigh?
The FHWA Federal Lands earthwork exhibit lists riprap rock, loose, at 1,550 kg/m³ and 2,610 lb per cubic yard. This calculator starts at 1,550 kg/m³. That displays as 1.31 short tons, 2612.61 lb, and 1.19 tonnes per cubic yard. The 2.61 lb gap against 2,610 is rounding: this site converts with 0.9144³ cubic meters per yard and 907.18474 kg per short ton. One short ton is 0.77 cubic yards.
What size is riprap?
Riprap is sized by class, not by an ASTM gravel number. Mile High Flood District classes by d50 are VL 6 inch, L 9 inch, M 12 inch, H 18 inch, and VH 24 inch, with specific gravity at least 2.5 and bulk density at least 1.3 ton per cubic yard. NHDOT 583 and FHWA HEC-23 name classes by nominal stone width: Class I 6 inch, Class III 12 inch, Class V 18 inch, Class VII 24 inch, and Class IX 36 inch. The 18 inch example is a thickness, not a claim that every class is 18 inch rock.
How much riprap for 30 by 8 feet at 18 inches?
The layer is 360.00 cubic feet, 13.33 cubic yards, and 10.19 cubic meters. At 1,550 kg/m³ that is 17.42 short tons and 15.80 tonnes. Allowance is 0.00 percent. One cubic yard at 18 inches covers 18 square feet, and 240 ÷ 18 = 13.33 cubic yards.
Is 1.31 tons per yard heavy enough for the MHFD minimum?
MHFD’s riprap specification asks for a bulk specific gravity that works out to at least 1.3 ton per cubic yard. This page’s 1.31 short tons per yard sits on that line. A short ton and the ton in that spec are the same 2,000 lb ton. If the quarry ticket is heavier, type that density. The 1,550 kg/m³ start is the FHWA loose figure, not a promise that every class weighs the same.
Do I need bedding under the riprap?
A filter or bedding layer is part of many bank jobs and it is not included in the 13.33 yards. Calculate that layer separately. It is a thinner, smaller stone. This tool is the riprap thickness you typed, over the area you typed, with no waste percent hidden in the answer.
How many truckloads is 17.42 tons?
The dump truck page is a planning tool, not a legal payload. A tandem preset of 14 tons would not hold 17.42 tons of this rock in one load. Two loads, or a heavier truck, is the planning read. Confirm the legal limit with the hauler. The ton figure itself is 17.42 at 1,550 kg/m³.
Can the bank be measured in meters?
Yes. A 9.14 m by 2.44 m area at 45.72 cm is the same 30 ft by 8 ft by 18 in, so the result stays 13.33 cubic yards, 10.19 cubic meters, and 17.42 short tons.