Measure the actual sloped surface, not just the flat map distance, then add specified thickness and toe trench volume.
Tools to have ready
- Tape measure
- Level
- Grade rod
- Project plans
- Slope safety gear
How to take the measurements
Measure horizontal run and vertical rise, or measure slope length directly.
Measure the protected width across the slope.
Enter the specified riprap layer thickness.
Add toe trench width and depth if shown on plans.
Use project stone class and density from the supplier or design.
Riprap slope section
- 1Slope surface length
- 2Riprap thickness
- 3Filter layer
- 4Optional toe trench
How the calculator works
Slope length = sqrt(run^2 + rise^2). Riprap volume = slope length x protected width x thickness.
Example: a 12 ft run and 5 ft rise creates a 13 ft slope length before multiplying by width and thickness.
What every field and unit means
Slope measurement
Choose how you measured the sloped face.
Use rise/run when you cannot safely measure along the slope.Horizontal run
Flat horizontal distance from top to toe.
Unit: ft or m. Measure on plan view or level ground projection.Vertical rise
Vertical height change of the slope.
Unit: ft or m. Measure elevation difference from toe to top.Slope surface length
Actual measured distance along the slope face.
Unit: ft or m. Lay a tape along the slope surface if safe.Protected width
Width of the slope or channel segment.
Unit: ft or m. Measure across the protected area.Riprap layer thickness
Average stone layer thickness.
Unit: in or cm. Use the project specification or stone size requirement.Toe trench width
Optional buried toe trench width.
Unit: ft or m. Enter 0 if no toe trench is used.Toe trench depth
Optional buried toe trench depth.
Unit: ft or m. Measure vertical trench depth in feet.Riprap bulk density
Bulk density including voids between larger stones.
Unit: lb/ft3 or kg/m3. Use supplier or specification value when available.Extra / waste
Percent added for cuts, spillage, edge cleanup, and small estimating errors.
Unit: percent. Use 5 percent for simple square work and 10 percent or more for irregular work. Do not enter 0 when the shape has curves, tapers, or hand trimming.Price per ton
Optional supplier price used to estimate material cost before delivery fees and taxes.
Unit: USD per US ton. Enter the quoted material price per US short ton. Leave 0 if you only need quantity.Assumptions and limits
- Slope surface area is larger than plan-view area.
- Stone sizing is an engineering decision.
- Large riprap has variable void space.
- Does not size stone for water velocity.
- Does not replace NRCS or engineer specifications.
- Unsafe slopes should be measured from plans.
Research basis: NRCS riprap guidance, NIST unit conversions. Full methodology and image-credit notes are maintained on the Editorial Policy page.