French Drain Calculator

Trench volume (length × width × depth) minus the pipe's volume, then converted to weight using gravel density (about 1.5 tons per cubic meter for washed drainage stone).

A residential trench is typically 8-18 inches wide and 18-24 inches deep, so the pipe sits below the water table you're draining.

A minimum 1% fall (about 1/8 inch per foot) keeps water flowing toward the outlet instead of pooling in the pipe.

Geotextile filter fabric stops fine soil particles from washing into the gravel and pipe over time, which would otherwise clog the drain.