Measure your area in square feet, multiply by your depth in feet, and divide by 27 to get cubic yards. Or skip the fractions and use a planning shortcut: 1 ton of standard landscaping rock covers roughly 80 to 120 square feet at 2 inches deep, so 100 sq ft per ton is a safe number to plan around at that depth.
That’s the math. Here is the plan:
- Decorative beds: 2 inches deep, about 100 sq ft/ton
- Garden beds and edging: 3 inches deep
- Pathways and driveways: 4 inches or deeper, for compaction and weight-bearing
Add a waste factor to your final number to allow for settling and uneven ground. Rock settles, ground is never perfectly flat, and running short mid-project means a second delivery fee you didn’t budget for.
Quick figure: A cubic yard of stone covers about 162 sq ft at 2 inches. That single number gets you through most residential jobs without opening a calculator app.
Key Takeaways
Accurate landscaping rock coverage comes down to one formula (area × depth ÷ 27), a 10% buffer, and a confirmed density figure from your supplier.
| Point | Details |
|---|---|
| Use the core formula | Area (sq ft) × depth (inches) ÷ 324 gives you cubic yards directly. |
| Remember the planning shortcut | 2 inches deep covers about 162 sq ft per cubic yard or 100 sq ft per ton. |
| Always add a buffer | Add 10% minimum, more on slopes or uneven ground, to avoid a second delivery. |
| Confirm density before ordering | Lava rock, river rock, and crushed granite all weigh differently per cubic yard. |
| Call in Rokworx for complex sites | Rokworx handles supply, delivery, and installation across Melbourne, including retaining walls and sloped or tight-access sites. |
Table of Contents
- Landscaping Rock Coverage Formulas You Can Actually Use
- How Much Rock Covers a Cubic Yard or Ton by Depth?
- Three Worked Examples for Common Yard Projects
- Does Rock Type Change How Much You Need to Order?
- Ordering, Delivery, and Avoiding a Second Trip
- Why Rokworx Handles the Coverage Math for You
- What the Calculators Get Wrong
- Get Landscaping Rock Delivered and Installed Right the First Time
- Sources
Landscaping Rock Coverage Formulas You Can Actually Use
Forget guessing. There are three formulas that cover almost every yard shape, and none of them require anything beyond a tape measure and basic arithmetic.
Step 1: Get your area.
- Rectangle or square: length × width
- Circle: π × radius² (radius is half the diameter)
- Triangle: 0.5 × base × height
Step 2: Convert depth to feet. Two inches is 0.167 feet. Three inches is 0.25 feet. Four inches is 0.33 feet.
Step 3: Multiply area × depth, then divide by 27. That gives you cubic yards, which is how most Australian suppliers quote bulk rock.
There’s a shortcut that skips the fraction conversion entirely: (Area in sq ft × Depth in inches) ÷ 324 = cubic yards. That 324 divisor comes from converting inches to feet and cubic feet to cubic yards in one step, and it’s the formula built into most online rock coverage calculators.
Pro Tip: Always order by volume, not weight, when you’re unsure of the exact rock type. Weight-based ordering assumes a fixed density, and density swings wildly between rock types. Volume doesn’t lie.
If your supplier only sells by the ton, ask them to convert your cubic yard figure using their specific product’s density. Don’t just apply a generic ton-to-yard ratio and hope for the best.
How Much Rock Covers a Cubic Yard or Ton by Depth?
Once you know your volume, you still need to translate it into what the supplier actually sells. Coverage per cubic yard is fixed math. Coverage per ton depends on the rock’s density, which is why the two numbers below aren’t perfectly interchangeable.
The cubic yard column is stable across almost every rock type because it’s pure geometry. The ton column moves depending on what you’re buying. A load of pea gravel, weighing in around 1.4 tons per cubic yard, covers differently than a denser crushed granite. Always confirm density with your supplier before locking in a tonnage order.
Planning number to remember: 2 inches deep, 162 sq ft per cubic yard, roughly 100 sq ft per ton. That combination handles the vast majority of decorative rock jobs without a single spreadsheet.
Three Worked Examples for Common Yard Projects
Numbers on a chart only help once you’ve run them against a real space. Here are three that cover most residential jobs.
1. Small decorative bed (6 ft × 4 ft, 2 inches deep)
- Area: 24 sq ft
- Volume: (24 × 2) ÷ 324 = 0.15 cubic yards
- Add a buffer for waste: 0.16 cubic yards, roughly 0.25 tons
- This is small enough that most suppliers will point you toward bagged product rather than a bulk load
2. 10 ft × 10 ft patio surround (3 inches deep)
- Area: 100 sq ft
- Volume: (100 × 3) ÷ 324 = 0.93 cubic yards
- With 10% buffer: just over 1 cubic yard, or approximately 1.4 tons
- Round up to a full cubic yard order. Suppliers rarely sell in fractional increments below that, and having a little extra beats a second delivery.
3. Driveway strip, 10 ft × 20 ft (4 inches deep)
- Area: 200 sq ft
- Volume: (200 × 4) ÷ 324 = 2.47 cubic yards
- With 10% buffer: about 2.7 cubic yards, or about three and a half tons
- Driveways often need a compacted base layer beneath the visible top course, so measure and order the two layers separately rather than treating it as one 4 inch pour.
Does Rock Type Change How Much You Need to Order?
Yes, and this is where a lot of DIY orders go wrong. Two rocks that look similar in a photo can have wildly different weights, which throws off any ton-based calculation.
Lava rock, for example, is remarkably light at around 0.65 tons per cubic yard, while granite and river rock typically run 1.35 to 1.5 tons per cubic yard. Order lava rock using a granite density assumption and you’ll come up short by close to half.
Shape matters too. Angular crushed stone locks together and settles less over time. Rounded river rock shifts more, especially on a slope, which is another reason the 10% buffer exists. Larger rocks also leave more air gaps between pieces, so a bed of 100mm rocks won’t give you the same solid coverage per cubic yard as a bed of 20mm gravel, even at the same depth.
Before you order:
- Ask the supplier for the specific product’s density in tons per cubic yard or cubic metre
- Confirm whether they sell by weight or by volume
- Request a sample if you haven’t seen the exact batch
- Adjust your order upward for lighter, larger, or more irregular rock
Pro Tip: If you’re torn between two similar-looking rock types, price them both by the cubic yard, not the ton. It’s the only apples-to-apples comparison that holds up regardless of density.
Ordering, Delivery, and Avoiding a Second Trip
Getting the math right doesn’t help if the delivery truck can’t reach your backyard. A few practical checks save real money.
- Bump your buffer above 10% on sloped or uneven sites, since settling eats into coverage faster on grades than on flat ground
- Bags make sense under about half a cubic yard or when access is too tight for a tipper truck
- One cubic yard is roughly 27 to 30 standard 40kg bags, so bulk almost always wins on cost past that threshold
- Ask about minimum bulk delivery quantities before you commit to a small order
- Confirm the truck can tip on your driveway or nature strip, and ask who’s responsible for barrowing rock from the drop point
Suppliers with real delivery experience, like this landscaping service’s project pages show, often flag access issues before the truck ever leaves the yard. That conversation upfront beats a truck stuck at your curb.
Why Rokworx Handles the Coverage Math for You
Getting the volume calculation right is one thing. Getting a delivery truck up a narrow Melbourne driveway, or knowing that a retaining wall needs a different base depth than a garden bed, is a different skill set entirely.
Rokworx supplies and installs landscaping rock across Melbourne, and the projects where a calculator alone falls short tend to share a pattern: steep slopes, tight access, large volumes, or a retaining wall that needs proper drainage and footing behind it. Ordering the right tonnage doesn’t help much if the site itself needs excavation first.
- Rock and stone supply with delivery across greater Melbourne
- Retaining wall construction, including sandstone and granite options
- Earthmoving and excavation for sites with tight access or steep grades
- Erosion control work for sloped properties where rock alone won’t hold ground
Getting the tonnage right on paper still leaves the hardest part unsolved: placement, drainage, and access. Projects with slope, scale, or structural load benefit from a site assessment rather than a calculator alone.
For larger loads or anything involving a retaining structure, a quick site visit answers questions a coverage chart never will.
What the Calculators Get Wrong
Most rock coverage guides hand you a formula and call it done. The formula is correct, but it assumes a flat, empty site and a rock type with predictable density. Neither is guaranteed.
The bigger gap is that quick planning figures like 100 sq ft per ton work fine for a weekend garden bed and can leave you noticeably short on a driveway or a sloped bank, where settling and compaction eat into coverage faster than a flat courtyard ever would. Homeowners who trust the shortcut without checking their specific rock’s density are the ones who end up making a second trip to the supplier.
What actually matters is sequencing: measure and calculate first, confirm density with whoever is selling the rock, and only then decide whether it’s a job for bagged product or a bulk delivery. Skipping the density check is the single most common reason DIY orders come up short, not bad math.
If there’s one thing worth prioritizing over any formula, it’s asking the supplier one direct question: what’s the density of this exact product? That answer, more than any calculator, determines whether your order lands right the first time.
Get Landscaping Rock Delivered and Installed Right the First Time
Running the numbers yourself is a solid starting point, but Rokworx turns that calculation into a finished result without the guesswork of matching density to your specific site. Rokworx supplies, delivers, and installs landscaping rock across Melbourne, handling everything from a small decorative bed to a full retaining wall build.
Browse the gallery of completed projects to see how coverage and depth play out on real Melbourne properties, or check the rock wall services page if your project involves a slope or structural retaining need rather than a flat garden bed. For material selection, the guide to popular landscaping rock types breaks down which stone suits which application.
Get in touch with Rokworx for a quote based on your actual site measurements, not just an online estimate.
Sources
- Crushed rock coverage (iSeekPlant)
- Mulch vs rock coverage and calculations (Jim’s Mowing)
- Landscape rock calculator (OmniCalculator)
- Gravel calculator and density guidance (WeGravel)
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