Landscape Rock Calculator
Tons of rock = length × width × depth (in) ÷ 324 × tons per yd³. A 20 × 10 ft bed 2 in deep takes 1.23 yd³, or 1.73 tons of river rock at 2,800 lb per cubic yard. Utah State University Extension gives 2 to 3 in for rock mulch; Colorado State gives 4 in to suppress weeds.
Rock needed
1.73 tons
1.23 yd³ · US short tons (2,000 lb)
- Volume
- 1.23 yd³ · 33.3 ft³ · 0.94 m³
- Weight
- 1.73 short tons · 3,457 lb
- Weight used
- 1.4 tons/yd³
- Bed area
- 200 ft²
Worked example
A 20 × 10 ft bed of river rock, 2 in deep
- 20 × 10 = 200 ft²; 200 × 2 ÷ 12 = 33.33 ft³
- 33.33 ÷ 27 = 1.23 yd³
- 1.23 × 2,800 ÷ 2,000 = 1.73 tons
Result: 1.23 yd³, about 1.73 tons of river rock.
Checked by the automated test “rock — 20 × 10 ft bed at 2 in = 1.23 yd³ = 1.73 tons of river rock”.
How it works
Volume (ft³) = length (ft) × width (ft) × depth (in) ÷ 12
Cubic yards = ft³ ÷ 27
Tons = cubic yards × rock weight (lb per yd³) ÷ 2,000
Assumptions
- Rock weights per cubic yard, dry, from Pacific Topsoils: cobble and 1 1/2 in drain rock 2,800 lb, pea gravel 2,800 lb, 5/8 in minus crushed rock 3,000 lb, pumice 1,080 lb.
- Other rocks, lava rock included, vary by source and size: pick « My supplier's weight » and enter the figure on the quote.
- Tons are US short tons (2,000 lb); metric results use tonnes. The volume is the loose rock delivered.
Reference table
| Depth | River rock, cobble | Crushed 5/8 in minus | Pumice |
|---|---|---|---|
| 1 in | 231 ft² | 216 ft² | 600 ft² |
| 2 in | 116 ft² | 108 ft² | 300 ft² |
| 3 in | 77 ft² | 72 ft² | 200 ft² |
| 4 in | 58 ft² | 54 ft² | 150 ft² |
At 2,800, 3,000 and 1,080 lb per cubic yard (Pacific Topsoils).
Rock bed or gravel base
- This page is for decorative beds. For a driveway or path base, the gravel calculator (linked below) uses crushed stone sold for that job.
- One rock per run. For a bed edged with cobble and filled with smaller rock, run the calculator once for each.
- Ask for the weight on the quote. Suppliers bill by their own scale; enter their tons per yard with « My supplier’s weight ».
Common mistakes
- Using one weight for every rock Pacific Topsoils lists 2,800 lb per yard for cobble and 1,080 lb for pumice: the same bed in pumice weighs 61 % less.
- Laying rock straight on the soil UC IPM suggests landscape fabric under rock mulch: it keeps stones from sinking into the soil and keeps soil, and weed seed, from moving up through the rock.
- Choosing large stones to stop weeds Colorado State University Extension says stones used as mulch should be under 1/2 in across to save water and hold back weeds; larger stones are mainly for looks.
Frequently asked questions
How many tons of rock are in a yard?
About 1.4 tons for cobble or drain rock (2,800 lb) and 1.5 tons for 5/8 in minus crushed rock (3,000 lb), per Pacific Topsoils. Pumice is about 0.54 ton.
How much river rock will I need?
Area in ft² × depth in inches ÷ 324 gives cubic yards; multiply by 1.4 for tons. One ton of river rock covers about 116 ft² at 2 in.
How much crushed rock do I need?
Same volume formula, with 1.5 tons per yard for 5/8 in minus crushed rock: one ton covers 108 ft² at 2 in. For a driveway base, use the gravel calculator.
How much does one cubic yard of river rock weigh?
Pacific Topsoils weighs cobble and drain rock at 2,800 lb per cubic yard, dry: 1.4 tons. If your supplier quotes another weight, pick My supplier's weight and enter it.
Sources
Formula, examples and sources checked on by the Yardstick Math team. How we check our formulas.
- Safe hauling of bulk materials – cubic yard weights (cobble 2,800 lb, crushed rock 3,000 lb, pumice 1,080 lb) — Pacific Topsoils, accessed
- Water-Wise Landscaping: Mulch (inorganic mulch 2 to 3 in deep) — Utah State University Extension, accessed
- Weed Management in Landscapes (landscape fabric under rock mulch) — University of California Statewide IPM Program, accessed
- Mulching (stones used as mulch smaller than 1/2 in) — Colorado State University Extension, accessed
- Handbook 44, Appendix C – General Tables of Units of Measurement (1 yd³ = 27 ft³; short ton = 2,000 lb) — NIST, accessed