How much rock do I need?
Area times depth is the volume. The weight of the rock turns that volume into tons, and tons are what a stone yard sells: the truck is loaded, weighed, and you pay for what the scale reads.
Worked example. 100 sq ft of river rock, 2 in deep.
- Volume: 100 sq ft × 2 in = 16.67 cu ft = 0.62 cubic yards
- Weight: 0.62 cubic yards × 1.3 tons = 0.80 tons (1,605 lb)
- In bags: 34 bags of 0.5 cu ft
- To order: stone goes by the tenth of a ton, so 0.9 tons.
A bed of 12 × 4 ft at 3 in is 12 cu ft, or 0.44 cubic yards. One cubic yard covers 162 sq ft at 2 in and 108 sq ft at 3 in.
What a yard weighs depends on the rock and on its size: the larger the stone, the more air between the stones.
| Material | Tons per cubic yard | Typical range | Source |
|---|---|---|---|
| River rock | 1.3 (2,600 lb) | 1.25 to 1.75 | Sands & Soils, Earthstone Rock, Stone Centers |
| Landscape rock | 1.4 (2,800 lb) | 1.3 to 1.5 | Earthstone Rock |
Suppliers do not agree, and each sells its own rock. Ask yours what a yard of the size you picked weighs, then press “Use my own figure”.
How deep should landscape rock be?
Deep enough that the ground, or the fabric, does not show between the stones. That depends on the size of the stone, and the two suppliers below work with these depths.
| For | Depth | In metric |
|---|---|---|
| River rock of 1 to 1 1/2 in | 2 in | 5 cm |
| Rock of 1 to 3 in | 3 in | 7.5 cm |
Mulch Mound: At 2 in deep a ton of small river rock (1 to 1 1/2 in) covers about 100 to 120 sq ft, and at 3 in about 65 to 80 sq ft; 1.4 tons per cubic yard is a safe conversion for river rock of 1 to 3 in.
Sands & Soils: A cubic yard of beige river rock weighs approximately 2,500 lb. It is sold small (3/8 in), medium (3/4 in) and large (1 to 3 in); the larger rock wants at least 3 in of depth.
Stone larger than 3 in needs more: measure a stone, and plan for a layer at least as deep as the stone is thick.
River rock, lava rock or gravel?
- River rock. Rounded stone, sold by size from 3/8 in up. It does not lock together, so it stays where it is laid on flat ground and wanders on a slope.
- Landscape rock. Crushed decorative stone, with edges. We weigh it at 1.4 tons a cubic yard (Earthstone Rock).
- Lava rock. Light and porous. The weights published for it differ by more than a factor of two, so the calculator gives its volume and its bags and no tons, until you type your supplier’s figure.
- Gravel. Pea gravel, crushed stone and driveway gravel are on the gravel and stone calculator, with a compacted base for driveways.
Fabric and edging
Landscape fabric goes under the rock, and edging round it. Tick “Landscape fabric under it” and each area gets a sheet of its own, cut square, 6 in past every edge: Lawn Love asks for 6 to 12 in wherever two pieces meet. The 12 × 4 ft bed takes 13 × 5 ft, 65 sq ft, and the calculator counts the rolls of the size you enter.
“Edging round every area” adds the length of the outer edge of each area: 32 ft for that bed. Both go on your list as lines of their own.
Two more things are counted from the same area:
- Flagstone is sold by what a ton covers, which depends on how thick the stone is. Hunker’s chart gives 100 sq ft a ton at 2 in thick; at that figure, 200 sq ft takes 2.00 tons. Type your stone yard’s figure over ours.
- Stepping stones are counted along the path, one for each stride. Mulch Mound puts a stride at 18 to 24 in from centre to centre: at 24 in, a path of 20 ft takes 10 stones.
Questions about rock
How much does a ton of river rock cover?
About 125 sq ft at 2 in deep, at 1.3 tons a cubic yard. Mulch Mound gives 100 to 120 sq ft for small river rock at that depth, and 65 to 80 sq ft at 3 in.
How many bags of rock make a yard?
54 bags of 0.5 cu ft make one cubic yard. For another size, divide 27 by the cubic feet printed on the bag.
How much does a yard of rock weigh?
River rock: about 2,600 lb, and from 2,500 to 3,500 lb in the sources we read. Landscape rock: about 2,800 lb. Wet rock weighs more.
Do I need fabric under rock?
It is a choice, not a rule. Fabric keeps the rock and the soil apart and lets water through. If you lay it, overlap the pieces and pin them: Lawn Love says a staple every foot along the edges and the overlaps.
Sources
- Sands & Soils, Beige River Rock. A cubic yard of beige river rock weighs approximately 2,500 lb. It is sold small (3/8 in), medium (3/4 in) and large (1 to 3 in); the larger rock wants at least 3 in of depth. Read on .
- Earthstone Rock, Cubic Yards vs. Tons for Landscape Rock. Landscape rock about 2,800 lb per cubic yard; river rock about 2,900 lb; sand about 3,000 lb; decomposed granite, landscape gravel and pea gravel about 2,700 lb; most rock between 1.3 and 1.5 tons per cubic yard. Read on .
- Stone Centers, Landscape Rock Calculator. River rock about 1.4 to 1.75 tons per cubic yard; lava rock about 1.2 to 1.4; sand 1.10 to 1.25. Read on .
- Mulch Mound, How Much River Rock Do I Need? Tons, Yards and Coverage. At 2 in deep a ton of small river rock (1 to 1 1/2 in) covers about 100 to 120 sq ft, and at 3 in about 65 to 80 sq ft; 1.4 tons per cubic yard is a safe conversion for river rock of 1 to 3 in. Read on .
- Hunker, How To Estimate Flagstone. A ton of flagstone covers 200 sq ft at 1 in thick, 150 sq ft at 1 1/2 in, 100 sq ft at 2 in and 75 sq ft at 3 in. Add 10 to 15% for sizing and waste. Read on .
- Lawn Love, How to Install Landscape Fabric Under Gravel. Keep a 6 to 12 in overlap between pieces of landscape fabric, and pin it with a staple every foot along its edges and overlaps. Read on .
- Charley’s Greenhouse & Garden, Contractor 20-Year Landscape Fabric, 3 ft x 50 ft Roll. Landscape fabric sold as a roll 3 ft wide and 50 ft long. Read on .
- Mulch Mound, Stepping Stone Path: How Much Stone to Order and How to Set It Right. A typical adult stride places the centre of each step roughly 18 to 24 in apart on flat ground: walk the path and measure your own. Read on .
Updated . How we calculate. Found a mistake? Tell us.