This landscape rock calculator shows how many cubic yards, tons and bags of rock to order for a bed, path or border: river rock, crushed rock, pea gravel or lava rock.
How to use the rock calculator
- Pick the type of rock. It only sets the weight per cubic yard; choose Other to enter your supplier’s figure.
- Choose a rectangle or a circle and enter the size of the area. Split odd shapes into simple pieces and add the results.
- Enter the depth of rock once it is spread, and keep a little extra for low spots.
- Enter the bag size if you are buying bags, and a price per ton, cubic yard or bag for a cost estimate.
Rock formulas
Volume (ft³) = length (ft) × width (ft) × depth (ft) Cubic yards = cubic feet ÷ 27 Tons = cubic yards × weight per yd³ (lb) ÷ 2,000 Bags = cubic feet ÷ bag size (ft³), rounded up
Rock is sold by volume (cubic yards or bags) or by weight (tons), so the calculator gives both. North Bay Materials lists sand, gravel, rock and river cobble at 2,500–2,900 lb per cubic yard, about 1.35 tons, and lava rock at 1,400–1,600 lb, about 0.75 tons. This page uses 2,700 lb for river rock and crushed rock, 2,800 lb for pea gravel and 1,500 lb for lava rock.
Worked example: a 20 × 8 ft river rock bed, 3 in deep
- Area: 20 × 8 = 160 ft².
- Volume: 160 × (3 ÷ 12) = 40 ft³, or 44 ft³ with 10% extra.
- Cubic yards: 44 ÷ 27 = 1.63 yd³.
- Tons: 1.63 × 2,700 ÷ 2,000 = 2.2 tons.
- Bags: 44 ÷ 0.5 = 88 bags of 0.5 ft³.
The same bed in lava rock is still 1.63 yd³ but weighs only 1.22 tons. A round bed 10 ft across and 2 in deep needs 0.48 yd³ before any extra.
How far does rock go?
A cubic yard covers 324 ÷ depth in inches square feet. A ton of heavy rock covers less ground than a ton of light lava rock:
| Depth | Area per cubic yard | Area per ton, river or crushed rock (2,700 lb/yd³) | Area per ton, lava rock (1,500 lb/yd³) |
|---|---|---|---|
| 2 in | 162 ft² | 120 ft² | 216 ft² |
| 3 in | 108 ft² | 80 ft² | 144 ft² |
| 4 in | 81 ft² | 60 ft² | 108 ft² |
| 6 in | 54 ft² | 40 ft² | 72 ft² |
Rock weight per cubic yard
| Rock | Weight per yd³ | Tons per yd³ | Cubic yards per ton |
|---|---|---|---|
| River rock or cobble | 2,500–2,900 lb | about 1.35 | about 0.74 |
| Crushed rock or gravel | 2,500–2,900 lb | about 1.35 | about 0.74 |
| Pea gravel | about 2,800 lb | 1.4 | 0.71 |
| Lava rock | 1,400–1,600 lb | about 0.75 | about 1.33 |
The ranges are North Bay Materials’ figures. The pea gravel weight is the one our pea gravel calculator uses, inside that range. Moisture, stone size and source all change the real weight, so ask your supplier for theirs.
Calculators for one kind of rock
The material pages add notes on sizes and uses: river rock, pea gravel, crushed stone, decomposed granite and gravel. To turn a supplier’s tons into yards, use the cubic yards to tons calculator.
Tips for ordering rock
- Ask how it is priced. Landscape yards usually quote per ton or per cubic yard, and garden centers sell bags. Enter the price in the same unit.
- Compare bags with bulk. One cubic yard is 54 bags of 0.5 ft³. Price a delivered yard against that many bags before you buy.
- Use your supplier’s weight. If they sell by the ton, ask what their rock weighs per yard and choose Other to enter it.
- Mark where the truck will dump. Keep a heavy load off septic tanks, sprinkler lines and soft lawn.
Questions
How much rock do I need?
Multiply length × width × depth in feet and divide by 27 for cubic yards. For tons, multiply by the weight per yard and divide by 2,000. A 20 × 8 ft bed 3 in deep takes 1.48 yd³, about 2 tons of river rock, before any extra.
How many square feet does a ton of rock cover?
About 80 ft² at 3 in deep and 120 ft² at 2 in for river or crushed rock at 2,700 lb per yard. Lava rock is lighter, so a ton covers about 144 ft² at 3 in.
How much does a cubic yard of rock weigh?
Typically 2,500–2,900 lb, about 1.35 tons, for river rock, gravel and crushed rock, and 1,400–1,600 lb, about 0.75 tons, for lava rock, according to North Bay Materials.
How many bags of rock make a cubic yard?
54 bags of 0.5 ft³, or 27 bags of 1 ft³, because a cubic yard is 27 ft³.
How many tons of rock for 100 sq ft at 2 in deep?
100 × 0.167 ft = 16.7 cu ft ÷ 27 = 0.62 yd, about 0.85 ton at 1.35 tons per yard.
Sources
- Landscape Materials Density Chart, North Bay Materials.
Used for: Weights per cubic yard for river cobble, rock, gravel, sand and lava rock. - NIST Guide to the SI, Appendix B.8: Factors for units listed alphabetically, National Institute of Standards and Technology.
Used for: Exact inch and foot definitions; cubic foot and cubic yard conversions.