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River Rock Calculator

Estimate river rock or other decorative stone for borders, beds and dry creek beds. Enter the area and depth to get cubic yards, tons and bags, with cost by the ton, yard or bag.

Quick examples
%

Extra for compaction, spillage and uneven ground.

lb/ft³

River rock is typically 90–105 lb/ft³ (1.2–1.4 tons per cubic yard); lava rock is far lighter.

$

Optional. Set to 0 to skip the cost.

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Volume needed0.39 yd³
Volume in cubic feet
10.5 cu ft
Estimated weight
0.53 ton
Area covered
60 ft²
Bags needed
21
Estimated cost
$63.00

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    Your recent calculations

    Results you calculate here are kept on this device so you can come back to them.

      Formula

      Volume (cu ft) = area (sq ft) × depth (in) ÷ 12 × (1 + waste %)
      Weight (lb) = cubic feet × density (100 lb/ft³ by default)
      Tons = pounds ÷ 2,000
      Cubic yards = cubic feet ÷ 27

      How to use it

      1. Choose the shape and enter the dimensions of the bed.
      2. Enter the depth; it should be at least twice the size of the stones.
      3. Change the density if your supplier gives tons per yard.
      4. Pick how the stone is priced and enter the price.

      Worked examples

      A 20 × 3 ft border, 2 inches deep, at $120 a ton

      Volume in cubic feet
      10 cu ft
      Volume needed
      0.37 yd³
      Estimated weight
      0.5 ton
      Bags needed
      20
      Estimated cost
      $60.00

      A triangular corner bed, 10 ft base and 8 ft height, 3 inches deep, 10% extra

      Volume in cubic feet
      11 cu ft
      Volume needed
      0.41 yd³
      Estimated weight
      0.55 ton
      Area covered
      40 ft²
      Bags needed
      22
      Estimated cost
      $66.00

      Depth depends on stone size

      Small ¾–1 in river rock: 2 in deep. 1–3 in rock: 3–4 in deep. Larger 3–5 in cobble is usually laid one stone thick, about 4–6 in. Too shallow a layer lets the fabric underneath show through.

      Lay landscape fabric first. It keeps the stone from sinking into the soil and makes weeds much easier to control.

      Coverage per ton

      At 100 lb per cubic foot a ton of river rock is 20 cubic feet. That covers about 120 sq ft at 2 in deep, 80 sq ft at 3 in and 60 sq ft at 4 in. Lava rock weighs roughly half as much, so a ton of it covers about twice the area.

      Questions people ask

      How much river rock do I need?

      Multiply the area in square feet by the depth in inches and divide by 12 for cubic feet. A 20 × 3 ft border 2 in deep needs 10 cubic feet, which is about half a ton or 20 bags of 0.5 cubic feet.

      How many square feet does a ton of river rock cover?

      About 120 sq ft at 2 in deep or 80 sq ft at 3 in deep, assuming 100 lb per cubic foot.

      How many bags of river rock equal a ton?

      About 40 bags of the 0.5 cubic foot (roughly 50 lb) size.

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