Riprap Quantity Calculator

Estimate the riprap quantity for a treated area from your designed layer thickness, with optional placed bulk density for weight.

Important

This calculator estimates quantity from dimensions you provide. It does not size or design riprap protection.

Riprap quantity calculator

Units
Treated area

Measure along the treated surface itself. On a slope, do not use map or plan dimensions — they understate the surface area.

How will you enter the area?
Layer thickness

Use the thickness from your design or specification. This calculator does not size riprap or choose a thickness.

Add any toe trench, key or overlap volume your design specifies. Leave blank if none.

Advanced optionsExtra material / handling allowance

Adds the percentage you choose to the order volume for waste, handling or contingency.

Result

Your result will appear here

Enter your treated area and designed layer thickness to see the placed riprap volume.

How this calculator works

The calculator multiplies the treated surface area by the layer thickness from your design, then adds any extra toe, key or overlap volume you enter.

Placed volume = Treated surface area × Designed layer thickness + Extra volume

Enter the area measured along the treated surface. The calculator does not convert plan dimensions and a slope angle into a surface area.

Weight is optional and needs a placed bulk density — the weight per volume of stone as placed, including the spaces between stones.

Riprap design limitations

Riprap protects slopes, banks and channels from erosion. Whether it works depends on hydraulic design: the flow it must resist, the stone size and gradation (often described by D50 and D100), the layer thickness and the underlying filter. This calculator does none of that.

Where the thickness comes from

In engineering practice the layer thickness follows from the selected stone gradation — FHWA and US Army Corps of Engineers methods, for example, relate it to D50 and D100 after hydraulic sizing. Enter the thickness your design specifies; the calculator will not choose one.

Measure the real surface

On a slope, the treated surface is larger than its footprint on a plan. Measure along the surface, or use an area from your design drawings.

Weight needs placed bulk density

Riprap products differ widely, and the density of solid rock is not the weight of placed riprap with voids between stones. There is no universal tons-per-yard figure for riprap; use the placed bulk density for your stone source.

For a decorative bed of large stone, use the Gravel Calculator instead.

Worked example

Example: 40 ft × 12 ft measured along the bank, 18 in designed thickness, 2 yd³ toe volume

  1. Treated area: 40 ft × 12 ft = 480 ft²
  2. Blanket: 480 ft² × 1.5 ft = 720 ft³ = 26.67 yd³
  3. With toe volume: 26.67 + 2.00 = 28.67 yd³

Result: 28.67 cubic yards placed. The thickness and toe volume are example inputs, not a design.

Frequently asked questions

What size riprap do I need?

Stone size comes from hydraulic design for your site. This calculator does not size riprap; ask an engineer or use your project specification.

How many US short tons of riprap do I need?

Calculate the placed volume, then enter the placed bulk density for your stone source. The weight is shown as an estimate.

Can I enter the slope angle?

No. Measure the treated surface directly, or take the area from your design drawings.

Sources & methodology

Placed volume is geometry from your design inputs. The riprap references below explain the design boundary and are never used as values. Sources relevant to this page: