French Drain Cost Calculator

How to plan a french drain budget

A french drain is a simple system: dig a trench, line it with fabric, drop in a perforated pipe, and backfill with drainage gravel. The budget lives in three places: how much gravel the trench swallows, how much perforated pipe it takes end to end, and whether you hire someone with a mini excavator or dig it yourself. This calculator asks for the measurements that drive those numbers and turns them into a materials list plus an optional labor total.

Sizing the trench and gravel

Residential french drains are usually 6 to 12 inches wide and 12 to 24 inches deep. The trench width times the depth times the length gives you gross volume in cubic feet. Divide by 27 for cubic yards. This calculator subtracts the space the pipe itself takes up, then multiplies by a waste factor before rounding up to the nearest half yard, which is how most yards actually sell gravel.

Pipe and fabric

The most common pipe is 4 inch perforated corrugated with a sock, sold in 10 or 100 foot rolls. Order enough to cover the full run plus a small waste allowance for cuts and fittings. Landscape fabric wraps the gravel to keep silt out; size it to cover the trench bottom, both sides, and enough overlap to fold across the top.

What is not in the price

Local material costs vary a lot. Bulk gravel is cheaper than bagged, and long delivery distances add fees. If your trench needs to cross concrete, tie into an existing storm line, or run through tree roots, expect real jobs to skew toward the high end of the range. Permits are cheap when they apply, expensive when you skip one and get flagged.

DIY vs hire

For short runs on flat ground with good access, DIY is straightforward. Beyond about 40 to 60 feet, or if the trench needs to be deeper than two feet, most people rent a trencher or hire it out. Leave labor at zero for a DIY plan; enter a per foot labor rate if you are comparing contractor bids.

This is a planning tool, not a contractor quote. Use it to size an order, sanity check a bid, and understand where the money goes before you break ground.