River Rock Calculator — Georgia

River rock is smooth, rounded stone worn by water. That rounded shape is the one trait that drives every decision you make with it. This calculator sizes a river rock bed by the loose depth you want to see, reporting both cubic yards and tons from the area and depth you enter.

Angular stone, such as crushed stone or road base, has sharp broken faces that catch on each other. Run a compactor over it and the faces lock, and the layer sets into a firm, stable surface. River rock does the opposite. Its smooth faces slide past one another, so the stones never interlock. A pile of river rock stays loose no matter what you do to it.

Because it does not lock, river rock rolls and migrates. It shifts underfoot when you step on it, creeps downhill on any slope, and works its way out of an open bed and onto the lawn or the walk over time. A bed with no edge slowly spreads and thins until it no longer reads as a clean stone layer.

This single trait sets up the rest of the job. River rock needs a firm border to hold it in place, and it needs landscape fabric under it so it does not sink into the soil. You do not compact it, because rounded stone has nothing to lock into. You rake it level to the depth you planned and let it lie loose.

So you order for the loose depth you want in the bed, with no compaction margin to add. The calculator reflects that. It sizes the volume from your area and target depth, adds a small overage for spread and settling, and reports the stone you need. The planning starts and ends with that loose, finished depth.

River rock comes in a range of sizes, and the size you pick sets both the look and the job the bed can do. Order one size and one stone type per bed, because mixed sizes in a single pile are hard to spread into an even layer.

Small stone, roughly 3/8 to 3/4 inch, sits in the pea-gravel range. It covers the ground well, fills a path or a narrow bed, and packs the most pieces into a given area. It reads as a fine, even surface and is the easiest size to rake level.

Medium stone, about 1 to 2 inches, suits general beds and borders. It gives a bolder look than the small grades and stays put a little better on flat ground, because each stone is heavier. It is a common choice for a decorative bed around a foundation or along a drive.

Large stone, roughly 2 to 5 inches, moves into cobble territory. It suits dry creek beds, drainage channels, and accent features where you want a rugged, natural look. Large stone also holds its place on a slope better than small stone, which washes and rolls off.

Match the depth to the size. A rough guide is a layer about two to three times the stone diameter, so the pieces seat in the bed rather than perch on the surface. Small stone covers at a shallow depth, while large stone needs a deeper layer to seat and hide the ground. Set the size first, then the depth, then read the totals.

The depth you choose answers two different questions: how the bed looks, and how well it holds back weeds. Decide which matters more for your bed, then set the depth to the deeper of the two needs.

For appearance, plan about 2 to 3 inches over landscape fabric. That depth hides the fabric, covers the soil, and reads as a finished stone bed. A layer thinner than 2 inches lets the fabric show through in spots and shifts underfoot, so the bed looks thin and unsettled.

For weed control, lean toward the deeper end or past it. A thicker layer of stone blocks more light from reaching the soil, and weed seeds below need light to push through. A thin, patchy layer lets light down and lets weeds find the gaps. Depth is your main lever against weeds that try to grow up through the bed.

Understand what the stone can and cannot do. A deep stone layer slows weeds from below, but it does not stop seeds that blow in and land on top of the stone. Those seeds root in the dust and debris that collect between the pieces over time. Fabric under the stone blocks the weeds rooted in the soil; the top-seeded weeds you pull by hand.

Match the depth to the stone size as well. Larger stone leaves larger gaps, so it needs more depth to cover the ground and shade the soil. When a bed has to both look finished and fight weeds, size it to the deeper requirement and keep the layer even, because a thin spot is where both problems start.

River rock rolls and migrates, so a bed only stays a bed if you contain it. Two steps do that work: a firm edge around the perimeter and landscape fabric underneath. Neither changes the tonnage the calculator gives you, but both decide whether the bed holds its shape.

Set an edge around the whole bed before the stone goes in. Metal, plastic, stone, or a buried timber all work as a border. The edge stops the rounded stone from creeping onto the lawn, the walk, or the beds next door. Without it, the bed spreads and thins until the stone no longer covers the ground it was meant to.

Mind the edge height against the stone depth. The finished stone layer should sit a little below the top of the edging. That keeps loose rock from spilling over the border and onto a path, where a stray stone rolls underfoot and turns an ankle or dulls a mower blade. Set the edge to the finished height and fill to just below it.

Lay landscape fabric across the cleared soil before the stone. The fabric blocks weeds rooted in the soil and keeps the rounded stone from working down into the dirt. Without it, the stone sinks into the soil over a season or two and weeds push up through the gaps, and you lose both the depth and the clean look.

Use a fabric rated for stone, not a thin film that tears under the weight. Overlap the seams by several inches and pin the fabric so it lies flat, because a lifted edge shows through the stone. Install the edge first, then the fabric, then rake the stone to depth. A contained bed over sound fabric is what keeps river rock looking placed rather than scattered.

River rock earns a second job in drainage, and it suits the work for the same reason it rolls. The rounded stones leave open gaps between them and never pack tight, so water flows through freely instead of clogging the way a fines-rich material would. This makes river rock a common choice for moving and slowing runoff.

A dry creek bed is the most familiar use. You dig a shallow channel along the path water already takes, line it, and fill it with river rock. The channel carries runoff during a storm and reads as a natural streambed when it is dry. Larger stone lines the bed and the banks, with the biggest cobble set where the flow is strongest.

Splash zones are a smaller version of the same idea. A bed of river rock under a downspout or along a roof drip line takes the force of falling water and spreads it, so it soaks in instead of cutting a trench in the soil. The gaps between the stones let the water down while the stone stays put and protects the ground.

Drainage features run deeper than decorative beds. A dry creek bed or a drainage channel fills a real trench several inches deep, not the shallow 2 to 3 inch cover of a ground-cover bed. The depth follows the drainage design and the volume of water, not a ground-cover rule, so measure the trench and size it on its own.

Size each drainage feature separately from any decorative bed in the same project. The depths are different, and averaging them shorts the channel and overfills the bed. Run the calculator once for the creek bed at its true depth, once for the surrounding cover at its depth, then add the totals.

Two practical points decide a lot of river rock projects: how it feels to walk on, and what it costs next to crushed stone. Both come back to the rounded shape.

River rock is hard to walk on, because the rounded stones roll and shift under a foot. Angular materials, such as crushed stone or decomposed granite, lock into a firmer surface you can stride across. River rock stays loose, so each step sinks and slides a little. For a path people use every day, that gets old fast.

Match the stone to the foot traffic. Small river rock walks better than large, because the smaller pieces shift less and a shoe bridges more of them at once. Large river rock and cobble are not a walking surface at all; they are for looks and drainage, and people turn an ankle trying to cross them. For a true walkway, a smaller grade over a firm base, or an angular material, serves better.

River rock also costs more than crushed stone, as a rule. It is a natural product worn smooth by water, then screened and often washed, so you pay for the rounded look and the sorting. Crushed stone is made by breaking larger rock, which is a cheaper process, and it lands in the yard at a lower price per ton.

So choose with both the look and the use in mind. When the rounded, natural look is the point and the bed is decorative, river rock is worth the premium. When a firm, walkable, lower-cost surface matters more than the look, crushed stone or decomposed granite may be the better pick. The calculator sizes any of them the same way, so the choice is about fit, not math.

Once you know the loose depth, the calculator turns your bed into both cubic yards and tons so you can order either way. A cubic yard is a block three feet on a side, or 27 cubic feet. A ton is a weight. The stone's density links the two, and for river rock that runs about 1.4 tons per cubic yard.

Treat that density as a planning figure, not an exact value. Rounded stone leaves gaps between the pieces, so a loose pile weighs less per cubic yard than solid rock would. The number also shifts with the rock type and the stone size. Ask your yard for the density of the exact product you buy if you order by the ton.

The key difference from angular base is that river rock takes no compaction margin. You do not pack it, so there is no shrink from a loose pile to a finished layer. You order for the loose depth you want in the bed. The calculator still adds a small overage, 10 percent by default, but that covers stone settling into the soil, spreading past the edge, and filling low spots, not packing.

Raise the overage on a slope or on rough ground. Rounded stone creeps downhill, so the low end of a sloped bed needs extra. Uneven ground swallows more stone than a flat bed. On a bed with many curves and cutouts, add a little more and round up, because a thin spot reads as unfinished.

Bulk river rock comes by dump truck, and one truck holds about 10 to 14 tons. Divide your total by that range to see the loads. Pick a drop spot close to the beds but off the planting area and the lawn, and lay a tarp under the pile so small stone does not work into the soil. Order one size per pile, and move the stone before long, because rain does not spoil it but a pile left sitting collects dust and weed seed.