Use this river rock calculator to find how many cubic yards, tons, and bags of rock you need. Enter the length and width of your area in feet, pick a depth, choose your rock size, and the calculator converts volume to weight using published density figures for each size class.
How to calculate river rock by hand
River rock is sold by the cubic yard or by the ton, and the math takes two steps: find the volume, then convert to weight.
cubic yards = length (ft) × width (ft) × depth (ft) ÷ 27\ntons = cubic yards × density (tons per cubic yard)Worked example: a 20 ft × 10 ft bed at 3 inches deep. Convert depth to feet (3 ÷ 12 = 0.25 ft), multiply 20 × 10 × 0.25 = 50 cubic feet, divide by 27 = 1.85 cubic yards. At 1.35 tons per cubic yard for 3/4–1 inch rock, that is 1.85 × 1.35 ≈ 2.5 tons.
River rock weight and coverage by size
| Rock size | Density (tons/yd³) | Coverage per ton at 2" | Coverage per ton at 3" |
|---|---|---|---|
| 3/8" pea-sized | 1.40 | ~115 sq ft | ~77 sq ft |
| 3/4"–1" | 1.35 | ~120 sq ft | ~80 sq ft |
| 1"–3" | 1.50 | ~108 sq ft | ~72 sq ft |
| 3"–5" large | 1.60 | — (lay 4"+ deep) | ~68 sq ft |
Densities vary between quarries. If your supplier publishes a tons-per-yard figure for the exact product, use theirs — the differences are usually within 10%.
How deep should river rock be?
Depth depends on rock size and purpose. For decorative ground cover with rock under 1 inch, 2 inches of depth hides the soil completely. For 1–3 inch rock, or anywhere you need durable coverage — borders, dry creek beds, drainage swales — plan on 3 to 4 inches. Very large rock (3 inches and up) needs a layer at least as deep as the largest stones, so 4 inches or more.
Going too shallow is the most common mistake: bare patches appear as rock shifts, and topping up later usually means paying a second delivery fee.
FAQ
How much does a cubic yard of river rock weigh?
About 2,700–3,200 lbs (1.35–1.60 tons) depending on size. Pea-sized rock runs ~1.40 tons/yd³; large 3–5" rock closer to 1.60.
How many square feet does a ton cover?
Roughly 60–80 sq ft at 3 inches deep, or 90–120 sq ft at 2 inches. Coverage drops as rock size and depth increase.
How deep should river rock be?
2 inches for small decorative rock, 3–4 inches for larger rock or full soil coverage, and at least one rock-diameter for stones over 3 inches.
Do I need landscape fabric underneath?
Usually yes — it keeps rock from sinking and blocks weeds. Skip it only where drainage into the soil is the goal.
How many bags make a cubic yard?
54 bags at 0.5 cu ft each. Bulk is typically 30–50% cheaper once you need more than half a yard.
Looking for other materials? See all our landscape material calculators.