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How Much Gravel for a 12×20 French drain?

The answer

9.78 ton

For a 12×20 ft french drain at 12" depth, with 10% overage included. Estimated cost: $538 at US national average pricing.

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With 10% overage
Or in 0.5 cu ft bag
Estimated cost (US avg)

How we calculated this

  1. 1. Area: 12 × 20 = 240 sq ft
  2. 2. Volume: 240 × (12/12) = 240 cubic feet
  3. 3. Convert + overage: Add 10% for waste → 9.78 ton
  4. 4. Cost: 9.78 × $55.00 ≈ $538

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