Landscape Rock Calculator: River Rock, DG & Decorative Stone Coverage
Choose from six decorative materials and a preset depth, and this calculator converts your bed size into cubic yards, bags, tons and cost as you type.
Enter your bed dimensions, depth, and stone type
Depth
Your results
Volume you need
0.49 cubic yards
13.3 cu ft
Area
80.0 sq ft
Weight
0.67 tons
1,333 lbs
Bags needed
27 bags
0.5 cu ft bags, rounded up
Estimated cost
-
Add a price to see cost
You need 0.49 cubic yards of river rock, about 0.67 tons, to cover 80.0 square feet at a 2-inch depth.
Material guide
Decorative Stone Properties
River rock is dense, naturally tumbled stone at about 100 lb/ft³, valued for its smooth, polished appearance in dry creek beds and borders. Decomposed granite weathers to a fine, gold-brown grit at 106 lb/ft³ that compacts into a stable, walkable surface, closer in behavior to a path material than a purely decorative one. Marble chips bring a bright white or grey-white finish at around 95 lb/ft³, popular for formal or Mediterranean-style beds.
Lava rock is the outlier of the group, porous volcanic stone at roughly 45 lb/ft³, less than half the density of the others, which means the same weight of it covers far more ground. Slate chips run about 85 lb/ft³ with a distinctive flat, layered shape and grey-blue-black coloring. White pebbles, similar in density to river rock at about 95 lb/ft³, give a cleaner, more uniform look than river rock's mixed tones.
Installation
Landscape Fabric Recommendation
Lay landscape fabric under any decorative rock bed before spreading stone. It's the single biggest factor in how much weed growth and material settling you'll deal with over the following years. Without it, stone gradually works its way down into the soil and weeds find their way up through it far sooner, both of which mean earlier top-ups and more frequent weeding.
Fabric works best paired with a shallow, purely decorative depth, around 1 inch, since the fabric itself is doing the weed suppression, not the depth of stone above it. Piling on extra depth over fabric adds cost without adding function.
Comparison
Mulch vs. Stone for Landscaping Beds
Mulch costs less to buy but breaks down within a year or two, needing replacement as it decomposes into the soil, which is actually a benefit for garden beds, since it improves soil structure as it goes. Stone costs more upfront but doesn't decompose, so a bed laid once can look the same for a decade, with only occasional raking to keep it tidy.
The trade-off that matters most is moisture: mulch holds water against the soil, which is good for thirsty plants but bad near a foundation, while stone sheds water and stays dry, which is the reverse. Many landscapes use both: mulch in planting beds, stone in borders, paths and drainage-sensitive areas near the house.
Related tools
Related Gravel Calculators
For a smaller, rounded stone better suited to paths and play areas than decorative beds, the pea gravel calculator uses the same coverage math with a density locked to that material specifically. If your project also needs a load-bearing surface, a path edge or a small parking pad, the crushed stone calculator covers the angular grades built for that.
For the complete site, including the full ten-material density table and a side-by-side cost comparison, visit the gravel coverage calculator homepage.
Answers
Frequently Asked Questions
How much landscape rock do I need for a flower bed?
Multiply your bed's area in square feet by your depth in feet, divide by 27, and you have cubic yards. A 10 ft by 8 ft bed at a 2-inch decorative depth needs about 0.49 cubic yards. For river rock at 100 lb/ft³, that comes to roughly 0.66 tons. This calculator does that math instantly as you enter your dimensions.
Should I use landscape fabric under decorative rock?
Almost always, yes. Fabric substantially slows weed growth and keeps the rock from working its way down into the soil over time, which is the main reason a decorative bed needs topping up every few years without it. It's a one-time cost that pays for itself in reduced maintenance.
Is mulch or stone better for landscaping beds?
Mulch is cheaper upfront, breaks down into the soil as a mild fertilizer, and needs replacing every year or two. Stone costs more initially but doesn't decompose, so a bed laid once can look the same for a decade with only occasional raking. Stone also doesn't hold moisture the way mulch does, which matters near a home's foundation but can work against you around moisture-loving plants.
What is the difference between lava rock and river rock?
Lava rock is porous volcanic stone, roughly a third the weight of river rock at around 45 pounds per cubic foot, which is why a truckload of it covers noticeably more ground than the same weight of river rock. River rock is dense, naturally tumbled stone at about 100 pounds per cubic foot, prized for its smooth, polished look rather than its light weight.
How deep should decorative landscape rock be?
A decorative depth of 1 inch is enough for most beds where the rock is purely visual, over landscape fabric. Standard beds typically use 2 inches for better weed suppression and a fuller look, and heavy-use areas, like a dry creek bed meant to actually carry runoff, go to 3 inches or more.
Do marble chips or white pebbles turn yellow over time?
Both can develop a slight yellow or dingy tint from dust, hard water residue, and organic buildup, though marble chips are somewhat more prone to it since marble is a softer, more porous stone. An occasional rinse with a hose extends the bright white look considerably; a mild outdoor stone cleaner handles more stubborn staining without harming the material.