Construction Calculator - Driveway and Sitework

French Drain Calculator

Estimate gravel volume for a French drain trench.

Reviewed: August 26, 2026

Calculate French Drain

For the French Drain Calculator, enter length, width, depth, waste allowance, material density, and material price. It multiplies length, width, and installed depth, converts to cubic yards, applies allowance once, and converts volume to tons through the entered bulk density.

Construction measuring tools arranged beside a residential building project

Formula used

Cubic yards = [length × width × (depth ÷ 12) ÷ 27] × (1 + waste ÷ 100); tons = cubic yards × density

French Drain Calculator measurement plan showing Length feet, Width feet, Depth inches

Worked french drain example

French Drain Calculator example: 38.8 ft × 10.6 ft × (4 in ÷ 12) ÷ 27 = 5.08 yd³ before allowance. After 10% allowance, the order basis is 5.59 yd³, or 8.1 short tons at 1.45 tons/yd³.

Volume, density, and supplier units

Use clean-stone density from the supplier and confirm whether the order will be by ton or cubic yard before scheduling delivery.

Field conditions that change tonnage

Trench overbreak, bedding below the pipe, aggregate above it, pipe displacement, fabric folds, and settlement influence stone quantity.

Questions specific to this calculation

Which bulk density belongs in the french drain tons estimate?

Enter trench length, actual trench width, and aggregate depth—not pipe diameter—then subtract displaced volume only if the project takeoff requires that precision.