Rip Rap Calculator

Rip Rap Calculator

A 50 ft × 6 ft area covered 12 inches thick needs about 11.1 cubic yards of riprap, roughly 16.7 tons at 1.5 tons per cubic yard. Layer thickness is usually 1.5–2 times the stone's D50 size. Enter your dimensions and stone class below.

Area & layer

Length (ft)

Width / slope length (ft)

Stone size class

Layer thickness (inches)

Density & waste

Density (tons per cu yd)

t/yd³

Waste / extra (%)

Price per ton (optional)

$/ton

Riprap needed

18.3tons

12.2 cu yd (incl. 10% waste).

Cubic yards

12.2 cu yd

Base (no waste)

11.1 cu yd

Show the math

area = 300 sq ft

cubic yards = area × (12 ÷ 12) ÷ 27 = 11.1

+ 10% waste = 12.2 cu yd

tons = 12.2 × 1.5 = 18.3

How to use this calculator

Enter the length and width (or slope length) of the area.
Set the layer thickness in inches.
Pick a stone size class, or enter a custom density.
Add a waste allowance for voids and uneven placement.
Read cubic yards and tons.

Formula

cubic yards = length × width × (thickness ÷ 12) ÷ 27
tons = cubic yards × density (≈ 1.5 tons per cu yd)
layer thickness ≈ 1.5–2 × stone D50

Worked example

A 50 ft × 6 ft area, 12 inches thick:

volume = 300 × 1 = 300 cu ft

cubic yards = 300 ÷ 27 = 11.1

tons = 11.1 × 1.5 = 16.7 tons

Rip rap calculator diagram of a stone layer on a slope with thickness labelled

Reference tables

Typical riprap stone classes

Class	D50 size	Layer thickness
Light / Class I	4–6 in	12"
Medium / Class II	9–12 in	18"
Heavy / Class III	15–18 in	27"

Classes and gradations vary by state DOT. Confirm against your local specification.

Tips & buying advice

Place riprap over a filter fabric or granular filter layer to stop the soil beneath from washing out.
Make the layer at least 1.5 times the largest stone thick so stones interlock.
Key the toe of a slope in below grade so the blanket does not slide.
Order about 10% extra — angular stone leaves voids and placement is never perfectly even.

For shoreline or channel work, follow your engineer or local permit requirements.

Frequently asked questions

How much area does a ton of riprap cover?

At 12 inches thick and about 1.5 tons per cubic yard, one ton covers roughly 18 square feet. Thinner layers cover more; a 6-inch layer covers about 36 square feet per ton.

What size riprap do I need?

It depends on flow velocity and slope. Light classes (4–6 inch stone) suit gentle ditches and low banks; heavier classes resist faster water. For channel or shoreline work, follow an engineer's or DOT specification.

How thick should riprap be?

Make the blanket at least 1.5 to 2 times the D50 stone size, and never less than the largest stone. A typical light riprap layer is about 12 inches; heavier classes are 18 inches or more.

Do I need filter fabric under riprap?

Almost always. A geotextile filter fabric or granular filter layer keeps the underlying soil from eroding out through the stone voids, which would undermine the riprap. Overlap seams generously.

How much does riprap cost per ton?

Riprap commonly runs about $45–$100 per ton delivered in 2026, depending on stone class, quarry distance and quantity. Get a local quote, since haul distance drives much of the cost.

Built and maintained by Sikander Mushtaq. Formulas checked against state DOT riprap gradation tables, USACE/FHWA riprap design guidance. See our methodology and sources, or learn about YardageMath.

Last updated: October 7, 2026

Estimates only. Confirm quantities with your supplier or contractor. Read the full disclaimer.