CalcMaterials

French Drain Gravel Calculator

Size the #57 drainage stone for your French drain trench in cubic yards and tons — and see the pipe and fabric you'll need to buy with it.

Calculate your materials

What you'll need to buy

  • #57 drainage stoneOpen-graded gravel that water flows throughShop
  • Perforated drain pipe4" corrugated or PVC, slotted/perforatedShop
  • Non-woven landscape fabricWraps the trench to stop silt cloggingShop
  • Pipe sock / filter sleeveExtra silt protection over the pipeShop
  • Drain grate / catch basinFor surface inlets where neededShop

Links marked Shop open a retailer search (Home Depot) and are affiliate links — we may earn a commission at no extra cost to you.

How the math works

A 50 ft trench, 1 ft wide, filled 12" (1 ft) deep with gravel = 50 cu ft. With 10% waste: 55 cu ft ÷ 27 ≈ 2.0 cubic yards ≈ 2.9 tons of #57 stone.

Formula

cubic feet = trench length × trench width × gravel depth (all in feet) cubic yards = cubic feet ÷ 27 tons = cubic yards × 1.4 (for #57 stone)

Reference values

Drainage stone density
MaterialDensity
#57 crushed stone≈ 1.4 tons / yd³
#8 pea gravel≈ 1.45 tons / yd³
3/4" clean≈ 1.35 tons / yd³
1 cubic yard= 27 cubic feet

Step by step

  1. Measure the trench length and width and decide the gravel fill depth.
  2. Multiply length × width × depth (in feet) for cubic feet.
  3. Divide by 27 to get cubic yards, then multiply by 1.4 for tons of #57 stone.
  4. Add 10% waste and round up to the next quarter-yard or ton.

Waste allowance

Always add a waste factor: more for diagonal, herringbone, or irregular layouts and for trenches in rocky soil. It's cheaper to round up than to pay for a second delivery.

Bags vs. bulk

Bagged material is convenient for small jobs, but loose/bulk delivery is almost always cheaper per unit once you pass roughly 1–3 cubic yards. Compare the per-cubic-yard price before deciding.

Frequently asked questions

How much gravel do I need for a French drain?

Multiply trench length × width × gravel depth in feet to get cubic feet, divide by 27 for cubic yards, then multiply by 1.4 for tons of #57 stone. A 50 ft × 1 ft × 1 ft trench needs about 2 cubic yards (≈2.9 tons) with waste.

What size gravel is best for a French drain?

Open-graded #57 crushed stone (about 3/4") is the standard choice because water flows freely through the gaps. Avoid fine gravel or sand, which clogs.

How many tons are in a cubic yard of gravel?

About 1.4 tons for #57 crushed stone. Density varies slightly by stone type and moisture, but 1.4 t/yd³ is the standard estimate used by most suppliers.

Do I need landscape fabric in a French drain?

Yes — wrap the trench (and ideally the perforated pipe) in non-woven landscape fabric to keep soil and silt from migrating into the stone and clogging the drain over time.

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