French Drain Estimator
Estimate gravel volume, pipe length, and filter fabric for a perforated-pipe french drain trench.
Limitations: Assumes a uniform rectangular trench. Catch basins, pop-up emitters, daylighting, and solid-pipe transitions are not included. Does not design drain direction or slope.
What to do next: Slope the trench 1–2% toward the outlet. Wrap the gravel in non-woven filter fabric to prevent silt infiltration. Use holes-down on perforated pipe so water can enter from below.
Planning estimate only. Drainage tied into a municipal storm system or a septic drainfield requires a permit and engineered design.