French Drain Materials Calculator
Estimate trench excavation, drainage stone, perforated pipe, geotextile fabric, fittings, and editable material cost.
How to use the french drain calculator
- Measure the actual project. Break irregular work into separate sections and record finished dimensions consistently.
- Enter the core measurements. The quick view focuses on project geometry; add or subtract sections where the calculator supports multiple areas.
- Review purchasing assumptions. Open Advanced inputs to replace example prices, waste, coverage, density, pack size, minimum order, or delivery assumptions with current project information.
- Calculate and verify. Review the formula, limitations, whole-unit rounding, product instructions, and supplier requirements before purchasing.
Key inputs covered: Drain length, Trench width, Trench depth, Pipe outside diameter, Pipe piece length, Stone and cut allowance, Fabric overlap, Fabric roll coverage, Drainage-stone example price, Pipe-piece example price, and additional project-specific assumptions.
Result coverage: The french drain calculator reports 7 separate quantities so the primary estimate and its supporting purchase or planning values can be checked together.
How the estimate works
Trench volume minus cylindrical pipe displacement estimates stone; fabric wraps the bottom and two sides plus overlap, while pipe and rolls round up to purchasable units.
Fabric cut width equals trench bottom width plus both side depths plus entered overlap.
Assumptions, rounding, and limitations
Dimensions are treated as finished measurements. Only deductions and allowances entered above are included. Decimal measurements display to two places; purchase quantities round up when a whole container or piece is required.
- This is a material takeoff, not hydraulic, geotechnical, grading, outlet, or erosion-control design.
- Confirm positive discharge, utility locations, trench safety, soil, fabric, stone gradation, pipe perforation/orientation, and local rules.
- Actual stone voids and compaction differ; supplier volume controls ordering.
Sources and review
These references support unit conversions and selected planning assumptions. Product instructions and local requirements control the actual project.
Last reviewed: 2026-10-09
Editorial process
BuildPlanCalc publishes the formula, editable assumptions, limitations, and supporting references so the estimate can be checked rather than treated as a black box. See the calculation and review methodology, or report a correction.
Frequently asked questions
Are the results exact?
No. Results are planning estimates based on the dimensions and assumptions entered. Confirm product coverage, site conditions, and ordering rules with the supplier.