Measure length × width of each bed area. Break irregular shapes into rectangles and add them. For multiple beds, enter the combined total.
Rock only covers open ground. Stand at the edge and estimate what fraction of the soil surface is covered by plant bases and spread.
Two inches is standard for decorative coverage. Rock doesn't decompose or compress like mulch, so a shallower layer maintains appearance long-term. Three inches for pathways or high-traffic areas where displacement is a concern. Four inches for drainage applications.
Only affects the ton conversion — not the cubic yard calculation. Different rock types vary significantly in weight. Lava rock is the outlier: its porous volcanic structure makes it roughly half the weight of gravel at the same volume.
Enter your material cost to see the total. Leave blank to skip.
Your Estimate
Tons (bulk order)
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Bags (0.5 cu ft)
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big box reference
Ordering
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Lava Rock Note
Lava rock is priced by volume at most suppliers, not by the ton, because of its low weight. If your supplier quotes a ton price, confirm whether they mean a dry ton by weight or a volume ton. The cubic yard figure above is the number to use — it's the volume your bed requires regardless of how the supplier prices it.
The square footage this calculator needs is a measurement, not an estimate.
Verdant Meridian traces the bed on-site with GPS — the output is the real number, not a curb-side guess. Plug that directly into this calculator and order right the first time.
Related Calculators
Common Questions
How many cubic yards of rock do I need?
Cubic yards = (open square feet × depth in inches) ÷ 324. At 2 inches deep, one cubic yard covers 162 square feet of open bed. Subtract the area your plants occupy before calculating — rock only covers open ground.
How do I convert cubic yards of rock to tons?
Multiply cubic yards by the weight of your rock type. Pea gravel and river rock run about 1.35–1.45 tons per cubic yard. Lava rock is the outlier at roughly 0.58 tons — its porous volcanic structure makes it about half the weight of gravel at the same volume.
How many bags of rock equal a cubic yard?
One cubic yard = 27 cubic feet. Standard 0.5 cubic foot bags = 54 bags per cubic yard. Rock bags are significantly heavier than mulch bags of the same volume — for most jobs over half a cubic yard, bulk delivery is more practical and cost-effective.
What depth should I use for decorative rock?
Two inches is standard for decorative coverage in a planting bed. Unlike mulch, rock doesn't decompose or compress significantly, so 2 inches maintains its appearance long-term. Three inches for pathways or high-traffic areas. Four inches or more for drainage applications.
Why does lava rock weigh so much less than other rock?
Lava rock is formed when molten rock cools rapidly, trapping gas bubbles inside. Those voids make the material porous and dramatically reduce its density compared to solid stone. The cubic yard requirement for your bed is the same regardless — it's a volume calculation. The weight difference only matters when you're ordering by the ton or hauling it yourself.
Al — Author of Field Notes
A farm kid who spent two decades building a landscape maintenance company. Writes for operators still in the truck, trying to figure out what comes next.