How Much Gravel for a French Drain?

Step-by-step method for sizing a french drain gravel order in cubic yards, tons, and bags of washed drainage stone.

A 100 ft french drain trench 12 inches wide by 18 inches deep holds about 150 cubic feet, or 5.6 cubic yards of washed drainage stone (about 7.5 tons). Order 6 cubic yards to allow for compaction and settling.

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The trench formula

Volume in cubic yards = (length ft x width ft x depth in) / 324. For a typical 12 x 18 inch trench, plan on 0.056 cubic yards per linear foot. Multiply by trench length and add 10 percent for waste.

Stone size

Use washed 3/4 to 1 1/2 inch drainage stone. Do not use gravel with fines (dust or sand). Fines clog the perforated pipe within a season or two.

Worked example: 60 ft trench

60 ft x 1 ft x 18 in / 324 = 3.33 cubic yards. Add 10 percent = 3.7. Order 4 cubic yards (about 5.4 tons).

Ready to run the numbers?

Use the french drain calculator to get a specific quantity for your project.