Rock Calculator
This rock calculator turns a bed, border or tree ring into cubic yards, tons and bags. A 30 × 4 ft bed covered 3 in deep needs 1.11 cubic yards of river rock (30 cubic feet); with 5% extra, that's 1.4–1.52 tons, 63 half-cubic-foot bags or a 1.5-yard bulk order.
Example: 30 × 4 ft at 3 in
1.5 cubic yards
- 1.4–1.52 tons
- 63 bags of 0.5 cu ft
- 31.5 cu ft
1.17 yd³ incl. 5% extra · rounded up to ½ yd
How much rock do I need?
Start with three measurements: the length and width of the bed in feet and the depth of rock you want in inches. Length × width gives square feet. Multiply that by the depth ÷ 12 for cubic feet, then divide by 27 for cubic yards. Suppliers sell rock by the cubic yard or by the ton, so the calculator also turns the volume into weight for the rock you pick. Changing the rock changes the tons and leaves the cubic yards alone: a yard of river rock weighs 1.2–1.3 tons per cubic yard, and a yard of lava rock only 0.51–0.63 tons per cubic yard.
- Area: 30 ft × 4 ft = 120 sq ft; × 3 in deep = 30 cu ft.
- 30 cu ft ÷ 27 = 1.11 cubic yards.
- Adding 5% extra for waste gives 1.17 cubic yards.
- Rounded up to the next 0.5 cubic yard: order 1.5 cubic yards.
- Weight of river rock: 1.4–1.52 tons, depending on moisture and grading.
Bought in bags, the same order is 63 half-cubic-foot bags. For beds that aren’t rectangles, pick Ring for a surround with a bare circle at the trunk, Circle for a round bed, Triangle for a corner bed or L-shape for a bed that turns a corner of the house. Use Known area if you already have the square footage. Add an area for each bed and the calculator totals them into one order.
Landscape rock for common beds and borders
The table starts with long, narrow borders of the kind that run along a fence or a foundation (3 × 20 ft, the 4 × 30 ft bed above and 5 × 50 ft), then two wider areas. Each cell leads with tons of river rock, followed by the bulk order in cubic yards and the half-cubic-foot bag count.
| Area | 2 in deep | 3 in deep | 4 in deep |
|---|---|---|---|
| 3 × 20 ft, 60 sq ft | 0.5 t , 0.5 yd³ · 21 bags | 0.7–0.8 t , 1 yd³ · 32 bags | 0.9–1 t , 1 yd³ · 42 bags |
| 4 × 30 ft, 120 sq ft | 0.9–1 t , 1 yd³ · 42 bags | 1.4–1.5 t , 1.5 yd³ · 63 bags | 1.9–2 t , 2 yd³ · 84 bags |
| 5 × 50 ft, 250 sq ft | 1.9–2.1 t , 2 yd³ · 88 bags | 2.9–3.2 t , 2.5 yd³ · 132 bags | 3.9–4.2 t , 3.5 yd³ · 175 bags |
| 10 × 20 ft, 200 sq ft | 1.6–1.7 t , 1.5 yd³ · 70 bags | 2.3–2.5 t , 2 yd³ · 105 bags | 3.1–3.4 t , 3 yd³ · 140 bags |
| 15 × 30 ft, 450 sq ft | 3.5–3.8 t , 3 yd³ · 158 bags | 5.3–5.7 t , 4.5 yd³ · 237 bags | 7–7.6 t , 6 yd³ · 315 bags |
Includes 5% extra, rounded up to the next half cubic yard, as the calculator does. Tons (t) span the sourced density range. Bags are 0.5 cu ft bags.
The cubic yards and bag counts hold for any rock in the calculator. Only the tons change, so pick lava rock or #57 stone above to see their weights for your own bed.
How much will 1 ton of rock cover?
A cubic yard covers the same ground whatever it’s made of. Coverage per ton varies, because a ton of light rock fills more cubic yards than a ton of heavy rock. At the same depth, a ton of lava rock spreads over roughly twice the area of a ton of river rock, and decomposed granite, which packs more weight into each yard, covers the least of the three.
| Depth | 1 cubic yard covers | 1 ton of river rock | 1 ton of lava rock | 1 ton of decomposed granite |
|---|---|---|---|---|
| 2 in | 162 sq ft | 125–135 sq ft | 257–316 sq ft | 108–120 sq ft |
| 3 in | 108 sq ft | 83–90 sq ft | 171–211 sq ft | 72–80 sq ft |
| 4 in | 81 sq ft | 62–68 sq ft | 129–158 sq ft | 54–60 sq ft |
Per-ton coverage spans the sourced density range: heavier material covers less.
Some suppliers convert with a single factor. Southwest Boulder & Stone, a decorative rock supplier, tells customers to multiply cubic yards by 1.25 to get tons for most landscape material, and names lava rock and mulch as the exceptions. The calculator uses each rock’s own weight range, so lava rock gets its own number.
How deep to lay landscape rock
Stone size matters most: bigger stones leave bigger gaps between them, so a layer of large river rock has to be deeper than a layer of pea gravel before the soil or fabric underneath stops showing through.
One bag is a cheap way to test a depth before you order in bulk. A half-cubic-foot bag spread over 3 sq ft makes a 2-inch layer, and over 2 sq ft a 3-inch layer. Lay one out at the depth you have in mind and look for bare ground between the stones.
For a path you walk on, the University of California’s garden path guidance gives 2 inches as the practical minimum, and 4 inches if thick stones or pavers will be set into it. The calculator questions any depth over 12 inches, in case a measurement in feet went into the inches box.
How much does a yard of river rock weigh?
A cubic yard of river rock weighs 1.2–1.3 tons per cubic yard, and the other rocks in the calculator differ more in weight than in anything else that affects your order. Each weight is a range drawn from lab tests, supplier weight tables and bag labels, all listed under Sources at the end of the page.
- River rock, the calculator’s default, comes as rounded stones of 1 to 3 inches. It usually goes into beds, dry creek beds and drainage.
- Lava rock is porous volcanic rock at 0.51–0.63 tons per cubic yard. We found fewer published weights for lava rock than for the other rocks here, so check the figure with your supplier if you’re buying by the ton.
- #57 stone is clean crushed stone of about 3/4 to 1 inch, at 1.25–1.29 tons per cubic yard. It drains well, and it’s also used under slabs.
- Decomposed granite is granite crushed fine enough to pack into a firm path, at 1.35–1.5 tons per cubic yard.
- Pea gravel and crusher run are in the picker as well, and the gravel calculator goes into both, along with driveways and base layers.
Lava rock: same yards, about half the weight
- Area: 30 ft × 4 ft = 120 sq ft; × 3 in deep = 30 cu ft.
- 30 cu ft ÷ 27 = 1.11 cubic yards.
- Adding 5% extra for waste gives 1.17 cubic yards.
- Rounded up to the next 0.5 cubic yard: order 1.5 cubic yards.
- Weight of lava rock: 0.6–0.74 tons, depending on moisture and grading.
The cubic yards and the 63 bags match the river rock bed, while the weight falls from 1.4–1.52 tons to 0.6–0.74 tons. You can feel the difference in the bags: a half-cubic-foot bag of Pavestone red volcanic rock weighs 19 lb, and the same size bag of Pavestone pea gravel weighs 45 lb.
Weight also sets how many trips a pickup makes. The example truck in the calculator, a 2026 Ram 1500 Tradesman with the 6′4″ box, is rated for a 2,360 lb payload. That covers about 0.91–0.98 cubic yards of river rock per trip, but about 1.87–2.28 cubic yards of lava rock, close to a level-full bed. This bed is two trips in river rock and one in lava rock.
If you buy lava rock by the ton, convert with lava rock’s weight. A general 1.25 tons per yard would turn the 1.17 cubic yards this bed needs into an order for 1.46 tons, and 1.46 tons of lava rock is 2.31–2.84 cubic yards, two to two and a half times what the bed needs.
Rock rings around trees
A ring is a circle with a smaller circle left bare in the middle. Measure straight across the outside of the ring, through the trunk, for the outer diameter. Then measure across the bare circle you’ll leave around the trunk. The calculator subtracts the small circle from the large one: area = π × (outer radius² − inner radius²).
- Area: π × ((6 ft ÷ 2)² − (1.5 ft ÷ 2)²) = 26.5 sq ft; × 2 in deep = 4.42 cu ft.
- 4.42 cu ft ÷ 27 = 0.16 cubic yards.
- Adding 5% extra for waste gives 0.17 cubic yards.
- Rounded up to the next 0.5 cubic yard: order 0.5 cubic yards.
- Weight of river rock: 0.21–0.22 tons, depending on moisture and grading.
The bulk order rounds up to half a cubic yard, nearly three times what this ring holds. Bags fit a job this size better: 10 half-cubic-foot bags, rounded up from 9.28. For several trees, add one ring per tree. The calculator adds the rings before it rounds, so three of these rings come to 28 bags, where rounding each ring on its own would give 30.
Bags vs bulk rock
Bagged rock comes in half-cubic-foot bags, so a cubic yard takes 54 of them. What those 54 bags weigh depends on the rock: 1,026 lb of Pavestone lava rock at 19 lb a bag, or 2,430 lb of Pavestone pea gravel at 45 lb a bag. On bigger beds the count climbs quickly: the 30 × 4 ft bed is 63 bags, and 200 sq ft at 3 inches is 105.
Once an order passes a yard or so, price it both ways: the bag count times the bag price, against a bulk price per ton or per yard plus delivery.
Weed barrier and edging
Landscape fabric is sold by area, so start from the bed’s square footage: 120 sq ft for the 30 × 4 ft bed and 26.5 sq ft for the tree ring, plus any overlap at the seams.
Edging is sold by length. Around a rectangle it’s 2 × (length + width), which is 68 ft for the 30 × 4 ft bed, or 38 ft if one long side runs against the house. Around a ring it’s π × the outer diameter: 18.85 ft for the 6 ft ring, plus 4.71 ft more if you edge the clear circle at the trunk too.
What landscape rock costs
Rock prices vary by type and by region. The gravel cost guide has prices per ton, per yard and per bag, and the cubic yards to tons converter helps when one supplier quotes by weight and another by volume.
Questions people ask
How do I calculate how much rock I will need?
Multiply length × width in feet for square feet, multiply by the depth in inches ÷ 12 for cubic feet, then divide by 27 for cubic yards. A 30 × 4 ft bed at 3 inches is 30 cubic feet, or 1.11 cubic yards. Add about 5% for spillage. If the yard sells by the ton, multiply by the rock's weight per yard: river rock runs 1.2–1.3 tons.
How much will 1 ton of rock cover?
One ton of river rock is 0.77–0.83 cubic yards. Spread 2 inches deep it covers about 125–135 sq ft, and at 3 inches about 83–90 sq ft. Lava rock is much lighter, so a ton of it covers about 171–211 sq ft at 3 inches.
How many tons is 1 yard of rock?
Multiply the cubic yards by the rock's weight per yard. River rock weighs 1.2–1.3 tons a yard, so 3 yards is 3.6–3.9 tons. Lava rock weighs 0.51–0.63 tons a yard, so the same 3 yards is 1.54–1.89 tons. Decomposed granite is heavier than both at 1.35–1.5 tons a yard.
How much does 1 yard of 57 stone cover?
A cubic yard of #57 stone covers 162 sq ft at 2 inches deep, 108 sq ft at 3 inches and 81 sq ft at 4 inches. A yard of any material covers the same area at the same depth. Only the weight of the yard changes from rock to rock, and for #57 stone it's 1.25–1.29 tons.
How much rock do I need for 200 square feet?
At 2 inches deep, 200 sq ft takes 1.23 cubic yards; with 5% extra, order 1.5 yards. At 3 inches it takes 1.85 cubic yards, so order 2. In river rock that's 1.56–1.69 tons at 2 inches or 2.33–2.53 tons at 3 inches.
How much lava rock do I need?
You need the same volume as with any other rock, so measure the area and depth as usual; only the weight differs. A 30 × 4 ft bed 3 inches deep needs 1.17 cubic yards with 5% extra: 0.6–0.74 tons of lava rock, against 1.4–1.52 tons of river rock. If you buy lava rock by the ton, convert with lava rock's own weight per yard.
Sources
- Graniterock, Southside 1 1/2" Round Rock (Tech Note). Accessed Oct 19, 2026.
- Graniterock, Southside 1" x #4 Round Rock (Tech Note). Accessed Oct 19, 2026.
- Roseville Landscape Material Supply (Roseville, CA), Landscape Materials Calculator - Material Weight and Coverage Reference. Accessed Oct 19, 2026.
- Do it Best (retailer), Pavestone 0.5 Cu. Ft. Decorative Landscape River Pebbles, Model #54250 (retailer listing). Accessed Oct 19, 2026.
- Landscape Centre Inc. (British Columbia, Canada), Bulk Materials: Lava Rock. Accessed Oct 19, 2026.
- Do it Best (retailer), Pavestone 0.5 Cu. Ft. Red Volcanic Rock, 19 Lb., Model #54341 (retailer listing). Accessed Oct 19, 2026.
- T.H. Kinsella, Inc. (Kinsella Quarries), Fayetteville, NY, Project Calculator - Materials & Pricing Estimates. Accessed Oct 19, 2026.
- Federal Highway Administration, Strength Characterization of Open-Graded Aggregates for Structural Backfills (FHWA-HRT-15-034), Chapter 3, Table 7. Accessed Oct 19, 2026.
- Do it Best (retailer), Quikrete 0.5 Cu. Ft. 50 Lb. All-Purpose Gravel (retailer listing). Accessed Oct 19, 2026.
- Expanded Shale, Clay and Slate Institute (ESCSI), Chapter 4: Proportioning Structural Lightweight Aggregate Concrete, Table 4.8. Accessed Oct 19, 2026.
- Ottr Landscape Supply (Boston, MA), Bulk Landscape Material Weight Guide: Dirt, Gravel, Mulch & More. Accessed Oct 19, 2026.
- Select Sand & Gravel (Texas/Oklahoma), Understanding Material Density: How Much Does a Yard of Landscape Rock Weigh?. Accessed Oct 19, 2026.
- Do it Best (retailer), Pavestone 0.5 Cu. Ft. 45 Lb. Pea Gravel, Model #54255 (retailer listing). Accessed Oct 19, 2026.
- Wisconsin DOT / Wisconsin Highway Research Program (Michigan State Univ. & Univ. of Wisconsin-Madison), Weight-Volume Relationships and Conversion Factors for Soils and Aggregates of Wisconsin (WHRP G22-05 Final Report, Dec 2023). Accessed Oct 19, 2026.
- Penn State Center for Dirt & Gravel Road Studies, Estimating Quantities and Costs (DGLVR Program webinar slides, 2/16/2023). Accessed Oct 19, 2026.
- Ram Trucks (Stellantis), 2026 Ram 1500 Specs (Tradesman 4x2 Quad Cab 6'4" box). Accessed Oct 19, 2026.
- The AMES Companies (AMES, Jackson, True Temper, UnionTools brands), Steel Wheelbarrows | Home by AMES. Accessed Oct 19, 2026.
- University of California Agriculture and Natural Resources, Gravel Pathways in the Garden (Earlene Millier, UC Master Gardener; Aug 4, 2011, reissued 2020-03-02). Accessed Oct 19, 2026.
- Southwest Boulder & Stone, Coverage Calculator (resources page). Accessed Oct 19, 2026.