French Drain Gravel Calculator

French Drain Materials Guide

A French drain is a trench filled with gravel and a perforated pipe that redirects water away from problem areas -- wet basements, soggy yards, retaining walls, and downspout discharge zones. The trench is typically 18-24 inches wide and 18-24 inches deep, lined with filter fabric to prevent soil from clogging the gravel.

The slope is critical -- without adequate slope, the drain becomes a puddle collector instead of a water mover. Minimum slope is 1% (1 inch of fall per 8 feet of run). More slope is better. Use washed crushed stone, not gravel with fines -- the fines will clog the system over time.

The Bottom Line

Free french drain calculator. Gravel volume, pipe length, and fabric for drainage trenches. Use this calculator to get an accurate estimate before purchasing materials or requesting contractor quotes. Accurate measurements save money and prevent project delays.