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French Drain Gravel Calculator

Estimate the gravel needed to fill a French drain trench. Enter the trench length, width and depth to get cubic yards and tons of drainage stone.

French Drain Gravel Calculator

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0
cubic yards
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tons
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bags (0.5 ft³)
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est. cost
French Drain Gravel Calculator, live preview
depth
Enter values to see your estimate.

How to Calculate French Drain Gravel

Change the calculator above and watch every figure and the diagram below update live.

Top-down view (area × depth)

W L depth 4"

Step 1 · Area

20 ft × 10 ft = 200 ft²

Step 2 · Volume (× depth, ÷ 27)

200 ft² × 0.33 ft ÷ 27 = 2.47 yd³

3.46
tons (× 1.4)
134
bags (÷ 0.5 ft³)

These figures update automatically as you change the calculator above.

Trench gravel coverage

Approximate coverage of one cubic yard of gravel at common depths.

Approximate coverage of one cubic yard of gravel at common depths.
DepthCoverage per yd³Relative coverage
1" 324 sq ft
100%
2" 162 sq ft
50%
3" 108 sq ft
33%
4" 81 sq ft
25%
6" 54 sq ft
17%
3 in
3"

At 3 inches deep, one cubic yard of gravel covers 108 sq ft.

French Drain FAQs

How much gravel do I need for a French drain?
Multiply trench length × width × depth (all in feet) and divide by 27 for cubic yards. A 40 ft × 1 ft × 1 ft trench needs about 1.5 cubic yards.
What gravel is best for a French drain?
Clean, angular stone like #57 works best, it has gaps for water to move through and won't clog with fines.
How deep should a French drain be?
Typically 8–24 inches deep and about 6–12 inches wide, sloped so water flows toward the outlet.
Do I need fabric with the gravel?
Yes, wrap the trench in landscape fabric to keep soil out of the gravel and maintain drainage over time.

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