River Rock Calculator

Enter your dimensions above and the calculator returns the answer in the units suppliers actually sell in — cubic yards, cubic feet, tons and bags.

Typical river rock depth by application

River rock is decorative rounded stone sold by the cubic yard or in bags; the size grade (3/4 inch, 1–3 inch, 3–5 inch) matters more than the colour for coverage.

What the numbers assume

The result uses a bulk density of 90 lb per cubic foot and a default waste allowance of 10%. Both are typical values, not measurements of your material — bagged products and different aggregate sources vary by 10% or more. Change the waste field if your subgrade is uneven or you are pouring against forms with complex edges.

Bigger stone covers less area per yard because the voids between the rocks are larger — a 3–5 inch grade needs roughly 20% more volume than pea gravel for the same depth.

Costs shown are material only, based on a national average price you can edit. They exclude delivery, short-form fees, equipment rental and labour.

The same yard covers different ground depending on stone size

If you have already worked out that a bed needs a yard of stone, the hard part is behind you. River rock is where that confidence breaks down: two people order the same cubic yardage, one bed looks finished, the other looks half empty. The difference is the grade — the size range the stone was screened to — and grade decides how much of that yard is rock and how much is air.

Bulk stone is sold by volume, but a cubic yard of stone is not a cubic yard of solid material. The spaces between the stones are part of the volume you paid for and none of the surface.

Those spaces behave differently at different grades. Pea gravel in the 3/4-inch range is roughly 60% stone and 40% void. A 3–5-inch cobble is closer to a 50/50 split, because rounded stones that size cannot nest into each other — they bridge, and every bridge leaves a pocket underneath. That is why this site's guidance says a 3–5 inch grade needs about 20% more volume than pea gravel for the same depth.

A yard of river rock covers about 162 sq ft at 2 inches deep, and that figure is quoted for the 1–3 inch grade the material table uses as its reference. Same yard, same 2 inches, but 3–5 inch cobble covers closer to 135 sq ft. Same weight, same invoice, 17% less bed. Order the smaller stone for anything you walk on, and the larger grade only where you are deliberately buying texture.

Working out your own number

The arithmetic is length × width × depth, with depth converted to feet, then divided by 27 for cubic yards. Keep one example in your head and every bed on your property becomes easy. A 12 × 12 ft bed at 2 inches deep:

• Area: 12 × 12 = 144 sq ft
• Depth in feet: 2 ÷ 12 = 0.167 ft
• Volume: 144 × 0.167 = 24.0 ft³
• Cubic yards: 24 ÷ 27 = 0.89 yd³
• With the 10% waste allowance the calculator applies: 0.98 yd³

Call it one yard, which is 2,400 lb — about 1.2 tons at the 90 lb per cubic foot bulk density published on the methodology page. The same bed at 3 inches rather than 2 is 36 ft³, or 1.48 yd³ with waste — a 50% jump for one extra inch. Depth is the multiplier people underestimate, and it is the first field worth changing in the river rock calculator before you commit to a grade.

Where the money actually goes

River rock is not expensive because it is scarce. It is expensive because it is processed. River rock is dredged or gathered from a deposit, washed to remove the silt and clay that would otherwise turn the bed to mud, then screened into tight size bands — 3/4 inch, 1–3 inch, 3–5 inch — each a separate product stockpiled and handled separately, much of it trucked in from river deposits rather than quarried locally.

That is the whole price story. Typical US prices run $80–130 per cubic yard for river rock against $35–65 for crushed stone: two to three times as much for less weight. The default $105 per cubic yard in the calculator is a national average and nothing more — type your supplier's number over it, because this is one of the most regionally variable materials on the site. That 12 × 12 bed at 2 inches is about $103 in river rock, against about $51 in crushed stone. If the bed is visible from the kitchen window that difference is easy to justify; behind a shed, probably not. Price both with the gravel calculator, since the depth and coverage math is identical.

Fabric: not optional, and no extra volume

River rock sinks. Rounded stone has no interlock and no fines to bind it, so every rain event works individual stones down into the soil below. In a bed without a barrier, a 2-inch layer of 1–3 inch stone is substantially gone within two seasons. You will not see it leave; you will just notice soil showing through, top it up, then do it again.

A woven geotextile stops that. It goes down over bare, raked soil after organic material and existing weeds are removed, with rock on top. Non-woven fabric also works and drains well. What does not work is bare soil, and what works badly is thin plastic that tears at every shovel nick and ponds water above the rock. Keep fabric clear of shrub crowns and tree trunks rather than wrapping them.

Fabric changes no volume, so it never appears in the calculator. It changes how long the bed lasts from about two seasons to a decade or more. Buy it by area with overlap: a 10 × 10 ft bed covered with 3-ft-wide fabric needs four runs of 10 ft plus 6 inches of overlap at each seam — 40 linear ft off the roll, about 43 linear ft on the invoice.

Dry creek beds have a depth profile, not a depth

A dry creek is a drainage feature with stone on top, which changes the shape of the calculation. Water does not sheet across it — it concentrates in the middle, so the middle runs deeper while the edges stay wide, shallow and slightly buried into the surrounding grade, letting the creek disappear into the lawn instead of sitting on it like a raised trough.

A creek with a 3 ft top width, 2 ft across the flat bottom and 12 inches deep in the middle has a cross-section of about 4.33 sq ft. Run that 40 ft long and you have 4.33 × 40 = 173 ft³, or 173 ÷ 27 = 6.4 yd³, and 7.1 yd³ with waste. Compare that with the naive 40 ft × 3 ft × 1 ft, which gives 4.4 yd³, and you can see why creeks come up short: the wide shallow edges are real volume and easy to forget.

Two to three inches of stone at the edges keeps the mower off loose rock; four to six inches of the larger grade through the middle handles the flow. Line the excavation with fabric, and if the creek carries real volume, put a perforated drain pipe under the deepest run before the rock goes in.

Stepping stones, borders, and small quantities

Between stepping stones the depth is about an inch and the gaps are small, but people over-order badly. Four 18-inch square stones set in a 12 × 12 ft area occupy 4 × 1.5 = 6 sq ft, leaving 138 sq ft of planting, and the joints are a fraction of that. At 1 inch deep across roughly 9 sq ft of joint you need 0.75 ft³ — under half a 2-cubic-foot bag. Border edging is the same story: a 3-inch-deep trench 8 inches wide along 60 linear ft is 4 ft² at 0.25 ft deep, or 1.0 ft³. Small areas are a bagged-material problem, and the bag premium is irrelevant when the whole job is two bags. Bagged pricing works the same way across loose materials, which is why the mulch calculator is worth a look if you are still choosing between bed coverings.

The honest advice is that river rock is a finish material with a finish price, and it earns that price only where you actually see it. Use it on the beds that frame the entrance and the walk, use crushed stone or mulch in the back reaches and along the side yard, and put fabric under all of it. Get the grade in writing before you order, because "river rock" on a yard's price sheet can mean anything from 3/4-inch pea to stone the size of your fist, and those two are not interchangeable.

Confirm the minimum-order and delivery terms before you commit, too — many landscape yards charge a trip fee on small loads that quietly doubles the cost of a decorative job, and it is worth knowing that number before you decide whether to fill a bed in one delivery or a bag at a time. If the coverage figure here and your supplier's disagree, the corrections route is how the data file gets fixed.