How Much Does a Ton of Rip Rap Cover? Chart by Thickness

How much does a ton of rip rap cover? Far less ground than gravel, because rip rap goes down in a thick layer of big stones. As a working figure, one ton of placed rip rap covers about 18 square feet at 12 inches thick, about 12 square feet at 18 inches and about 9 square feet at 24 inches. This guide shows where those numbers come from, gives a coverage chart by layer thickness, explains how stone size sets the thickness and walks through how many tons to order for a ditch, a pond bank or a shoreline.

The short answer

Working figure: one ton of rip rap fills roughly 18 cubic feet once it is placed, voids included, or about 2/3 of a cubic yard.
Coverage = 18 ÷ layer thickness in feet. That gives about 36 sq ft at 6 inches, 18 sq ft at 12 inches, 12 sq ft at 18 inches and 9 sq ft at 24 inches.
Thickness is set by the stone size, not by how far you want the stone to stretch. Bigger rock needs a thicker layer, so coverage per ton drops as the stone gets larger.
Order extra. Uneven ground, a keyed-in toe and stone that does not nest perfectly usually call for about 10 percent more than the bare math.

Rip rap coverage per ton by layer thickness

The chart assumes rip rap that weighs about 1.5 tons per cubic yard as placed, the middle of the 1.4 to 1.6 range used in our riprap sizes and weight guide. The range column shows the spread from heavier, tighter-packed stone to lighter or more open placement.

6 inches thick: about 36 sq ft per ton (34 to 39)
9 inches thick: about 24 sq ft per ton (23 to 26)
12 inches thick: about 18 sq ft per ton (17 to 19)
18 inches thick: about 12 sq ft per ton (11 to 13)
24 inches thick: about 9 sq ft per ton (8.4 to 9.6)
30 inches thick: about 7 sq ft per ton (6.8 to 7.7)
36 inches thick: about 6 sq ft per ton (5.6 to 6.4)

Turned around, that is about 5.6 tons for every 100 square feet at 12 inches, 8.3 tons per 100 square feet at 18 inches and 11.1 tons per 100 square feet at 24 inches.

Why a ton of rip rap covers so little

Solid rock is heavy. Rip rap is usually quarried from dense stone such as granite, limestone or basalt, and solid stone of that kind weighs somewhere around 150 to 180 pounds per cubic foot. A pile of large, angular stones is not solid, though. The gaps between them take up a good share of the volume, so a cubic yard of placed rip rap weighs noticeably less than a cubic yard of solid rock, which is why the working figure lands near 1.5 tons per cubic yard.

Even so, one ton is only about 18 cubic feet. Spread that 12 inches deep and you have a patch a little over 4 feet square. Compare that with a ton of driveway gravel spread a few inches deep, which can cover 80 square feet or more; see how much a ton of crushed stone covers.

The formula

Area = length × width in feet, measured along the slope, not flat on a map.
Volume in cubic yards = area × layer thickness in feet ÷ 27.
Tons = cubic yards × about 1.5, or use your supplier’s tons-per-yard figure if they give one.
Add about 10 percent for the toe, uneven subgrade and stone that does not pack tightly.

If you only need square feet per ton, divide 18 by the thickness in feet. For metric jobs, a tonne of placed rip rap at about 1.78 tonnes per cubic meter fills roughly 0.56 cubic meters, so it covers about 1.9 square meters at 300 mm thick.

How stone size sets the layer thickness

On engineered work, layer thickness comes from the stone gradation. Federal Highway Administration guidance for riprap revetment (HEC-11) says the layer should be no thinner than the diameter of the largest stones, or 1.5 times the median stone size (D50), whichever is greater. It also calls for at least about 1 foot (300 mm) for practical placement, and 50 percent more thickness when the rock is placed underwater. Some state design manuals use 2 times the median size instead of 1.5.

In practice that means:

Light rip rap with a median size around 6 to 8 inches usually goes down about 12 inches thick, so plan on roughly 18 sq ft per ton.
Medium rip rap with a median size around 12 inches needs about 18 inches or more, so about 12 sq ft per ton.
Heavy rip rap with a median size of 18 inches or larger needs roughly 27 to 36 inches or more, so about 6 to 8 sq ft per ton.

Thinner 6 to 9 inch layers of small stone show up in landscaping, around downspout outlets and in small swales, but they are not a substitute for a designed revetment where water moves fast.

Worked examples

Drainage ditch, 3 ft wide × 60 ft long, 12 inches thick: 180 sq ft ÷ 18 = 10 tons, plus 10 percent = about 11 tons.
Pond bank, 4 ft high on a 2:1 slope, 50 ft long, 18 inches thick: the slope length is 4 × 2.24 = about 9 ft (measured on the face), so the area is about 450 sq ft. 450 ÷ 12 = 37.5 tons, plus 10 percent = about 41 tons.
Culvert outlet apron, 8 × 12 ft, 12 inches thick: 96 sq ft ÷ 18 = 5.3 tons, plus 10 percent = about 6 tons.
Shoreline, 100 ft long × 10 ft of slope face, 24 inches thick: 1,000 sq ft ÷ 9 = 111 tons, plus 10 percent = about 122 tons, which is several full dump truck loads.

Measuring a slope correctly

Rip rap is usually placed on a bank, so measure the length of the slope face, not the flat distance across it. If you know the bank height and the slope ratio, multiply the height by the factor for that slope:

1.5:1 slope: height × 1.80
2:1 slope: height × 2.24
3:1 slope: height × 3.16

Add the width of any toe trench, where the bottom row of stone is dug in below the streambed or ground line, because that rock counts too.

Don’t forget what goes under it

Rip rap needs a filter underneath, usually geotextile fabric rated for rock placement, a bedding layer of smaller graded stone, or both. A bedding layer is a separate order with its own tonnage; for a 6-inch layer of crushed stone, the crushed stone calculator will give you the tons. Our post on separation fabric under a driveway base covers how fabric keeps soil and stone apart.

Ordering and hauling

Ask for the class or gradation, not just “rip rap.” Quarries and state transportation departments use their own class names and size ranges.
Ask what the yard uses for tons per yard. If they quote a figure for their stone, use it in place of 1.5.
Plan for heavy loads. Even a small job runs to several tons, and individual stones can weigh hundreds of pounds; see how much a boulder weighs. Rip rap is normally delivered by dump truck rather than hauled in a pickup; see how many tons fit in a dump truck.
Check permits. Placing rock in or along streams, lakes and wetlands often needs local, state or federal approval before work starts.

Common mistakes

Using gravel coverage numbers for rip rap and ordering a fraction of what the job needs.
Choosing a thin layer to save tons, which leaves the large stones sticking out and the filter exposed.
Measuring the bank on a flat plan instead of along the slope face.
Leaving out the toe trench and the bedding stone.
Ordering by the cubic yard from one supplier and by the ton from another without converting.

Questions people ask

How many square feet does a ton of rip rap cover?

About 18 square feet at 12 inches thick, 12 square feet at 18 inches and 9 square feet at 24 inches, using a placed weight of about 1.5 tons per cubic yard. Heavier, tightly packed stone covers a little less.

How many cubic yards is a ton of rip rap?

Roughly two thirds of a cubic yard, or about 18 cubic feet, once it is placed with the gaps between stones included. At 1.4 to 1.6 tons per yard the range is about 0.63 to 0.71 cubic yards per ton.

How many tons of rip rap do I need?

Multiply the area in square feet, measured along the slope, by the layer thickness in feet, divide by 27 for cubic yards and multiply by about 1.5. Add about 10 percent for the toe and uneven ground.

How thick should rip rap be?

Federal Highway Administration guidance for revetments calls for a layer at least as thick as the largest stones or 1.5 times the median stone size, whichever is greater, and at least about 1 foot. Underwater placement gets 50 percent more.

Does bigger rip rap cover more area per ton?

No. A ton fills about the same volume whatever the stone size, but larger stones need a thicker layer, so each ton covers less ground.

How many tons of rip rap per 100 square feet?

About 5.6 tons at 12 inches thick, 8.3 tons at 18 inches and 11.1 tons at 24 inches, before adding extra for waste and the toe.

Related guides

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