Landscape Rock Calculator
Work out how many tons or bags of river rock, lava rock, cobble, or marble chips your landscaping project needs. Enter your dimensions below.
Measure straight across the widest point.
Adjust depth below if needed.
Covers spillage and compaction. 5–10% is normal.
Everything is calculated in your browser. Nothing you type is sent anywhere or stored.
Bags or bulk delivery?
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Coverage & weight
Material profile
A standard 20 ft × 10 ft bed at the typical 3 inch depth needs 2.5 tons of river rock, or 2.75 tons with 10% waste added. Weight varies a lot by material — the same bed needs only about 1.4 tons of lighter lava rock, but roughly 2.6 tons of denser marble chips or cobble.
Landscape rock needed for common project sizes
Weight varies a lot by rock type, so tonnage for the same footprint differs between lava rock and river rock or cobble.
| Project | Depth | Cubic yards | Tons |
|---|---|---|---|
| Small border strip, river rock, 15 × 1.5 ft | 2 in | 0.14 yd³ | 0.19 tons |
| Standard bed (site default), river rock, 20 × 10 ft | 3 in | 1.85 yd³ | 2.50 tons |
| Same bed, lava rock, 20 × 10 ft | 3 in | 1.85 yd³ | 1.39 tons |
| Path topping, marble chips, 25 × 3 ft | 2 in | 0.46 yd³ | 0.65 tons |
| Large accent bed, cobble, 30 × 15 ft | 3 in | 4.17 yd³ | 5.73 tons |
| Long drainage border, river rock, 60 × 3 ft | 3 in | 1.67 yd³ | 2.25 tons |
Landscape rock types, density and typical use
| Type | Weight per yd³ | Best for | Drainage |
|---|---|---|---|
| River rock | 2,700 lb | Beds, borders, drainage | Good |
| Lava rock | 1,500 lb | Decorative beds, mulch alt. | Excellent |
| Cobble (4–8″) | 2,750 lb | Accent borders | Excellent |
| Marble chips | 2,800 lb | Decorative landscaping | Good |
Figures are for dry material. Wet or freshly delivered material can weigh noticeably more.
How to calculate landscape rock you need
- Measure your bed, border, or path, in feet, separately for each area if depths differ.
- Choose your rock type, river rock, lava rock, cobble, or marble chips — weight per yard varies widely.
- Set the depth, 3 inches for beds, 2 inches for borders and path toppings.
- Add 10% waste, for irregular edges and spillage during placement.
- Review tons and bags, then decide between bulk delivery and bagged material based on total volume.
Worked example
Here’s the math for the site default: a 20 ft × 10 ft decorative bed at a 3 inch depth, using river rock (2,700 lb/yd³), with 10% waste added.
- Area20 ft × 10 ft = 200 sq ft
- Depth in feet3 in ÷ 12 = 0.25 ft
- Volume200 × 0.25 = 50 cu ft
- Cubic yards50 ÷ 27 = 1.85 yd³
- Tons (river rock, 2,700 lb/yd³)1.85 × 2,700 ÷ 2,000 = 2.5 tons
- Plus 10% waste2.5 × 1.10 = 2.75 tons
- Order amountRound up to 3 tons in bulk, or about 110 bags at 0.5 cu ft each
Recommended depth by project
| Project | Recommended depth | Notes |
|---|---|---|
| Border edging strip | 2 in | Site default for borders; enough to define the line without excess cost |
| Path or walkway topping | 2 in | Matches border depth; lay over a compacted base or fabric |
| Standard decorative bed | 3 in | Site default; covers soil or fabric completely with larger stone sizes |
| Large cobble accent bed (4–8 in stone) | 4–5 in | Bigger stones need more depth so the bed doesn't look sparse |
| Lava rock mulch bed | 2–3 in | Lightweight material spreads further per ton than heavier rock |
| Drainage bed/French drain surround | 4–6 in | Deeper layer improves water movement around the drain pipe |
Bags or bulk delivery?
A $6.50 bag covering 0.5 cu ft works out to about $13 per cubic foot. Bulk river rock at $60/ton runs about $3.00 per cubic foot, and lighter lava rock is even cheaper per cubic foot in bulk since a ton covers more volume. Once a job needs more than about 7.5 cubic feet — roughly 15 bags — bulk delivery is cheaper even after the flat delivery fee.
- Small accent area or potted plants (under 5 cu ft):bags are simplest and keep waste to a minimum.
- Medium bed or border (5–40 cu ft):compare bag count vs. bulk-plus-delivery; bulk usually wins past about 15 bags.
- Large bed or multiple areas (40+ cu ft / 1.5+ yd³):order bulk delivery, and ask about split loads if you’re using more than one rock type.
Common mistakes
- Choosing one rock size for the whole yardsmall chips wash away on slopes while large cobble looks out of scale in small borders; match size to the space.
- Ordering lava rock using a river rock tonnage estimatelava rock is roughly half the weight of river rock per cubic yard, so a tonnage figure sized for river rock way overbuys lava rock.
- Skipping fabric under porous lava rockorganic debris and weeds settle into the pores faster than in solid stone, and fabric slows this down.
- Underestimating depth for large cobbleanything under 4 in of coverage looks thin and lets the stones roll or separate.
- Not separating bed and border quantitiesbeds (3 in) and border edging (2 in) need different depths; calculate them separately rather than using one blended average.
- Forgetting drainage directionrock beds on a slope need a defined low point or drain, or water channels under the rock and erodes the soil beneath it.
What this calculator assumes
Adjust your result if your project differs from these.
- Depth is measured after the rock has settled, not the loose-poured height.
- Lava rock density is significantly lower than solid stone; recalculate tonnage separately if mixing rock types.
- Waste allowance covers irregular bed edges and spillage during placement, not long-term loss.
- Bag size is assumed at 0.5 cu ft; verify against your supplier’s actual bag size.
- Calculation assumes a single rock type and depth per area; multi-zone yards should be calculated zone by zone.
- Pricing is a national average estimate; heavier stone like cobble and river rock typically costs more to deliver than lighter material.
Common questions
What's the difference between river rock, lava rock, cobble, and marble chips?
River rock is smooth, rounded stone around 2,700 lb/yd³; lava rock is porous and much lighter at about 1,500 lb/yd³; cobble is larger (4–8 in) rounded stone; marble chips are small, polished, and denser at about 2,800 lb/yd³.
How deep should landscape rock be?
3 inches for a standard bed, 2 inches for borders and path toppings — go deeper (4–5 inches) for large cobble so it doesn’t look sparse.
Do I need landscape fabric under rock?
Yes, in most cases. Fabric keeps rock from sinking into soil and slows weed growth, though it’s especially important under porous lava rock, where debris settles into the pores over time.
Is lava rock cheaper than river rock?
Often, and it also covers more area per ton since it’s roughly half the weight of river rock — a bed that needs 2.5 tons of river rock needs only about 1.4 tons of lava rock.
How much does a ton of landscape rock cover?
At a 3 inch depth, one ton covers about 80 sq ft of river rock or about 144 sq ft of lava rock, since lava rock weighs much less per cubic yard.
Can I mix rock sizes in the same bed?
You can, but it usually looks more intentional to use one primary size per bed and reserve a second size for borders or accents rather than blending randomly.
Does landscape rock need to be replaced or topped up?
Rarely needs full replacement, but expect to top up every few years as rock settles, gets kicked out of beds, or gets buried under mulch and debris.
How do I stop landscape rock from sinking into the soil?
Lay landscape fabric before placing the rock — it creates a barrier between the stone and soil so the rock stays on the surface instead of gradually sinking in.
What rock is best for a drainage area?
River rock or cobble — both have excellent drainage characteristics and are heavy enough to stay put in a drainage swale or around a downspout.
Bags or bulk for landscape rock?
Bags work fine under about 15 bags (roughly 7.5 cu ft); past that, bulk delivery is cheaper even after the flat delivery fee, especially for denser materials like cobble or river rock.
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Project
| Shape | — |
| Dimensions | — |
| Depth | — |
| Area | — |
| Material | — |
| Waste allowance | — |
Volume & weight (incl. waste)
| Cubic yards | — |
| Cubic feet | — |
| Weight | — |
| Tons (rounded up) | — |
Shopping list
| Bulk order | — |
| Bagged alternative (0.5 cu ft) | — |
| Estimated cost | — |
Notes
Estimate generated by materialcalculate.com. Assumes uniform depth and standard dry material densities. Confirm quantities with your supplier before ordering.