About the River Rock Calculator
River rock is stone that has been tumbled smooth by water, giving it rounded edges and attractive colours from grey and tan to rust and black. It is used for dry creek beds, borders along foundations, drainage swales and low-maintenance planting beds. Unlike gravel, it comes in a wide range of sizes, from small pebbles to fist-sized cobbles, and that size changes how much stone you need: bigger stones must be laid deeper to cover the ground below.
This river rock calculator works out the tons of rock for a bed by stone size. Choose the size and enter the bed's length and width, and it fills in a sensible depth for that size, then gives the weight in tons, the cubic yards, how many square feet one ton covers, the number of bags, and the landscape fabric to lay underneath.
How to Use the River Rock Calculator
Choose the stone size. The depth updates to about twice the typical stone.
Enter the bed length and bed width in feet.
Adjust the depth in inches if you want a thicker or thinner layer.
The Formulas
area = length × width
volume = area × depth ÷ 12
tons = volume ÷ 27 × 1.35
coverage = 20 ft³ per ton ÷ (depth ÷ 12)
fabric = area × 1.1Step-by-Step Example
A 30 × 4 ft bed of 1–3 in river rock, 3 inches deep.
area 30 × 4 = 120 ft²
volume 120 × 3 ÷ 12 = 30 ft³ = 1.11 yd³
tons 1.11 × 1.35 = 1.5 tons
coverage one ton covers about 80 ft²
bags 30 ÷ 0.5 = 60 bags
fabric 132 ft²Matching Depth to Stone Size
A single layer of large stones leaves gaps between them, and soil or fabric shows through. As a rule of thumb, lay river rock about twice as deep as its typical size so the stones overlap and hide what is below. The calculator suggests 2 inches for ¾–1½ inch rock, 3 inches for 1–3 inch, 5 inches for 3–5 inch and 8 inches for 4–8 inch cobbles. You can go deeper for a fuller look, but extra depth adds weight quickly, and it does little for appearance once the ground is covered.
Coverage per Ton
Suppliers sell river rock by the ton, so it helps to know how far a ton goes. A ton of river rock occupies about 20 cubic feet. Spread 2 inches deep it covers about 120 square feet, at 3 inches about 80, at 5 inches about 48 and at 8 inches only about 30 square feet. That is why a cobble bed needs several times as much stone as a pebble bed of the same area.
Dry Creek Beds
A dry creek bed is a shallow channel lined with river rock that carries rainwater away from the house or simply looks like a natural stream. Dig a swale 6 to 12 inches deep and two to three times as wide, lay fabric, and line it with a mix of sizes: larger cobbles along the edges and in bends, smaller rock in the bottom, and a few boulders for interest. Calculate each size separately using the area it will cover. If the channel carries real runoff, set the stones firmly so flowing water does not wash them downhill.
Landscape Fabric and Edging
A woven or non-woven landscape fabric beneath the rock suppresses weeds and stops stones sinking into soft soil, which keeps the layer looking full for years. Overlap joins by about 6 inches and pin them every few feet; the calculator adds 10% for overlaps. Around plants, cut an X in the fabric rather than a large hole. Edging of steel, stone or concrete keeps rock out of lawns and makes mowing easier.
Bags or Bulk
Garden centres sell river rock in bags of about 0.5 cubic feet, convenient for small accents and container tops. Bulk from a landscape yard is much cheaper per ton and comes in more sizes and colours. For anything over about half a ton, a delivery is usually worth it.
Using Mixed Sizes
Many of the best-looking beds mix two or three sizes. Larger stones read as the main feature, while smaller ones fill the gaps and stop weeds finding light. To plan a mix, split the bed into the areas each size will cover, or estimate the share of each, and run the calculator once per size. Boulders are usually bought individually rather than by the ton, so add them separately. Set the largest stones first, partly buried so they look settled, then fill around them with the smaller rock, working towards the edges.
Around the House
River rock along a foundation keeps soil from splashing onto siding and stops mulch from holding moisture against the wall. Slope the ground away from the house before laying fabric and rock, so water drains outward, and keep the stone a few inches below any siding, vents or termite inspection strips. Rock reflects heat, so plants beside it need to tolerate warmer, drier conditions than they would under bark mulch.
Understanding Your Result
The headline is the tons of river rock for your size.
The volume line gives the area, depth and cubic yards.
The coverage line shows how many square feet each ton covers and the bag count.
The fabric line gives the landscape fabric with overlaps.
The depth check line says whether your depth suits the stone size.
When Should You Use This Calculator?
Use it when planning a rock border, bed or dry creek.
Use it to compare the stone needed for small pebbles against cobbles.
Use it to order fabric along with the stone.
Common Mistakes
Laying large stones too thin. Use about twice the stone size.
Skipping fabric. Weeds grow up and rock sinks into soil.
Mixing up tons and cubic yards. A cubic yard weighs about 1.35 tons.
Placing rock against siding. Leave a gap so water and insects cannot reach the wall.