How this calculator works
It calculates the volume of your slope or drainage area from length, width and depth, converts that to cubic yards, then to tons using a typical riprap weight of about 1.4 tons per cubic yard.
Worked example — a 30 ft × 6 ft streambank section at 12 inches deep:
30 × 6 × (12 ÷ 12) = 180 cubic feet → ÷ 27 = 6.67 cubic yards → × 1.4 = 9.33 tons.
30 × 6 × (12 ÷ 12) = 180 cubic feet → ÷ 27 = 6.67 cubic yards → × 1.4 = 9.33 tons.
How thick should a riprap layer be?
Layer thickness should run about 1.5–2× the diameter of the largest stone in the mix, which usually works out to 9–24 inches depending on the riprap class and how much erosion energy the slope needs to handle.
Frequently asked questions
How many tons of riprap per cubic yard?
About 1.4 tons per cubic yard, though larger, more angular classes can run slightly heavier or lighter depending on void space.
How deep should a riprap layer be?
Typically 1.5–2 times the largest stone diameter — commonly 9–24 inches for slope and streambank protection.