River Rock Calculator
Work out how much river rock or decorative stone you need in yards and tons, with coverage adjusted for the stone size you are buying.
How much river rock do I need?
River rock is ordered by the ton almost everywhere, even though you measure the job in square feet and think about it in inches of depth. The chain is straightforward: area times depth gives you cubic feet, divide by 27 for cubic yards, then multiply by the weight per yard to get tons.
For most decorative stone that weight is around 2,800 pounds per cubic yard, so one cubic yard of river rock is roughly 1.4 tons. At three inches deep, a yard covers about 108 square feet, which means one ton covers somewhere near 75 to 80 square feet.
| Area | 2 in deep | 3 in deep | 4 in deep |
|---|---|---|---|
| 100 sq ft | 0.9 tons | 1.3 tons | 1.7 tons |
| 250 sq ft | 2.2 tons | 3.2 tons | 4.3 tons |
| 500 sq ft | 4.3 tons | 6.5 tons | 8.6 tons |
| 1,000 sq ft | 8.6 tons | 13.0 tons | 17.3 tons |
Stone size changes your coverage
Here is the thing most calculators get wrong. River rock is sold in size bands, and the band changes how the stone packs. Small 3/8 inch pea sized stone nests tightly with very little air space. Large 3 to 5 inch cobble leaves big voids between pieces.
Practically, that means a ton of large cobble covers noticeably more ground than a ton of small stone at the same nominal depth, but the layer is less stable and weeds find the gaps faster. It also means you cannot go thin with big stone. A 2 inch layer of 3 inch rock is not a layer, it is a scattering, and you will see fabric through it.
Rough guide for depth by stone size:
- 3/8 to 1/2 inch: 2 inches is enough for a border, 3 for full coverage.
- 3/4 to 1 inch: 3 inches minimum. This is the most popular size for beds and dry creek beds.
- 1 to 2 inch: 3 to 4 inches.
- 2 to 5 inch cobble: at least 4 inches, and usually laid as a single visible layer over a base.
Not all decorative stone weighs the same
Lava rock is the trap here. It looks like stone, it is sold alongside stone, and it weighs less than half as much. If you calculate a lava rock job using a generic 2,800 pounds per yard you will order roughly twice the tonnage you need and pay for it.
| Stone | lb per cubic yard | Tons per yard | Note |
|---|---|---|---|
| River rock | 2,600 to 3,000 | about 1.4 | Rounded, does not lock together |
| Crushed stone #57 | 2,600 to 3,000 | about 1.4 | Angular, better on slopes |
| Pea gravel | 2,700 to 2,900 | about 1.4 | Migrates badly on any grade |
| Marble chips | 2,500 to 2,900 | about 1.35 | Raises soil pH over time |
| Lava rock | 1,000 to 1,400 | about 0.6 | Less than half the weight of normal stone |
Rock does not need a compaction allowance
If you have used a gravel calculator before you may have seen an allowance added for compaction. That applies to base material like crusher run, which contains fine particles that settle and lock when you run a plate compactor over them. Decorative river rock has no fines and never gets compacted, so what you order is what you get. This calculator does not add compaction for rounded decorative stone, and does add it when you pick a base material.
Put fabric down, and pick the right kind
Stone sinks. Without a separation layer, a three inch bed of river rock over bare soil becomes a two inch bed with a lot of dirt in it after two seasons, and then weeds root directly in the accumulated silt.
Use a woven geotextile rather than the thin non woven landscape fabric sold in garden centres. Woven fabric is what actually holds up under the weight of stone. The cheap stuff tears when you rake and breaks down in a few years. Overlap the seams by at least six inches and pin it properly, because any gap is where the stone starts disappearing.
One honest warning. Fabric does not stop weeds forever. Organic matter blows in, settles between the stones and becomes a seedbed sitting on top of your fabric. Expect to blow the bed out with a leaf blower once or twice a year, and plan on refreshing the stone every five to seven years on an exposed site.
Getting it home
Stone is the heaviest thing most homeowners ever order. A single cubic yard is around 1.4 tons, which is already at or past the payload of a half ton pickup. Three yards is over four tons and needs a proper dump truck.
If you are hauling yourself, one yard per trip in a full size truck is the realistic limit, and you should expect the yard to load you light for exactly that reason. For anything over two yards, the delivery fee is cheaper than the suspension work.
Common questions
How many tons of river rock do I need per square foot?
At 3 inches deep, one ton of river rock covers roughly 75 to 80 square feet. So a 500 square foot bed needs about 6.5 tons. Larger stone sizes cover a little more per ton because they pack with more air space between pieces.
How much does a yard of river rock weigh?
Around 2,600 to 3,000 pounds, so roughly 1.4 tons per cubic yard. Lava rock is the exception at 1,000 to 1,400 pounds per yard, which is less than half.
How deep should river rock be?
Two to three inches for small stone under half an inch, three inches for the common 3/4 inch size, and four inches or more for large cobble. Going thinner than the stone size itself means you will see the fabric underneath.
Do I need landscape fabric under river rock?
Yes, and use woven geotextile rather than thin non woven fabric. Without it the stone works down into the soil and you lose depth within a couple of seasons. Fabric slows weeds but does not stop them permanently, since debris builds up on top of the stone and germinates there.
Is river rock cheaper in bags or bulk?
Bulk, by a wide margin, and it crosses over faster than mulch does. A 0.5 cubic foot bag holds very little stone, so a single cubic yard is 54 bags. Even with an $85 delivery fee, bulk usually wins past about half a yard.
These figures are planning estimates. Bulk material weight shifts with moisture and screen size, and suppliers round differently, so confirm the final quantity with your yard before you order.