Estimate French drain materials and drainage performance. Calculate trench volume, gravel needed, landscape fabric area, perforated pipe length, drainage slope, total fall, runoff flow, and capacity margin for yard drainage, foundation drainage, and stormwater drainage planning.
Materials estimate:
The calculator estimates trench volume, gravel volume, pipe length, and landscape fabric area.
Slope and fall:
The calculator converts your slope into total fall over the drain length.
Runoff capacity check:
The calculator estimates stormwater runoff from rainfall, drainage area, and runoff coefficient.
Drain rock storage:
The calculator estimates temporary water storage in the void space between drain rock.
A French drain calculator helps estimate the materials and drainage values needed before digging a trench or buying gravel, pipe, and fabric.
It can help compare trench volume, gravel yards, pipe length, fabric area, slope, total fall, runoff flow, and storage capacity.
Your result shows estimated gravel, pipe, fabric, slope, total fall, runoff, and storage values for planning. Actual French drain performance depends on soil type, trench depth, pipe outlet, groundwater conditions, surface grading, clog protection, fabric type, local code, and where the water is discharged.
A French drain is a gravel-filled trench, often with perforated pipe, used to collect and redirect water away from wet areas, foundations, yards, or retaining walls.
Multiply the trench length by width by depth to get trench volume, then subtract pipe volume if desired. Convert cubic feet to cubic yards by dividing by 27.
Many French drains are planned with a slight slope toward the outlet. The required slope depends on site conditions, pipe layout, outlet elevation, and local requirements.
No. This calculator gives a planning estimate. Final design should account for soil, water volume, outlet location, trench depth, pipe type, fabric type, and local drainage rules.