Skip to calculator
MaterialCalc

—online—visits

MaterialCalc — French Drain Gravel & Pipe Calculator

Estimate prepared 09/01/2026. Estimates only; verify against your plans before ordering.

French Drain Gravel & Pipe Calculator

Twelve inches is standard. Wider drains more water.

Deep enough to get below what you are protecting.

%

Trench walls slump and stone settles.

Result

Loading…

A french drain is a trench full of washed stone with a perforated pipe at the bottom, and the stone is the expensive part — several tons for even a short run. This works out the tonnage, the pipe lengths, and the filter fabric that keeps the whole thing from silting up.

Assumptions used

These are the numbers behind the result. Where one of them is soft, the cost range widens rather than pretending to a precision the data does not have.

Crushed gravel density
105 lb/ft³

Compacted 3/4 in crushed stone. Varies by quarry and moisture; loose stone runs lighter.

USGS aggregate bulk density range — Industry standard, varies by supplier, checked 09/01/2026

Perforated pipe length
10 ft

Home Depot / Lowe's published product data — Published product data, checked 09/01/2026

Filter fabric width factor
1.6

The fabric wraps the trench and folds over itself at the top, so it is wider than the trench.

Standard drainage practice — Industry standard, varies by supplier, checked 09/01/2026

French drain trench width
12 in

Standard drainage practice — Industry standard, varies by supplier, checked 09/01/2026

French drain trench depth
18 in

Standard drainage practice — Industry standard, varies by supplier, checked 09/01/2026

Prices verified 09/01/2026 (US national average, big-box retail shelf price and regional ready-mix quotes). Regional adjustment: Blended from RSMeans city cost index bands and BLS construction wage differentials.

The formula

Trench volume = length × width × depth. Deduct about 8% for the pipe, add a settlement allowance, then convert to tons at 105 lb per cubic foot. Fabric = length × (width + twice the depth) × 1.6 for the overlap at the top. Pipe comes in 10 ft lengths.

Worked examples

60 ft drain along a foundation, 12x18 in trench

Drain length: 60 Trench width: 12 Trench depth: 18 Waste: 20

About 4 tons of stone, 6 lengths of pipe and 250 ft² of fabric. The stone alone is a delivered truckload.

100 ft drain across a wet yard, 12x24 in

Drain length: 100 Trench width: 12 Trench depth: 24 Waste: 20

Around 9 tons. Deeper trenches drain better but the tonnage climbs proportionally — depth is what makes long drains expensive.

30 ft curtain drain, 18x18 in

Drain length: 30 Trench width: 18 Trench depth: 18 Waste: 20

Wider and shorter — about 3 tons. A wide trench intercepts more subsurface flow, which is what a curtain drain is for.

Choosing materials

  • Use washed #57 stone. Crusher run and other stone with fines in it packs solid and the drain stops working within a couple of seasons — the fines are exactly what you are trying to keep out.
  • Pipe goes in holes-down. Water rises into the pipe from the stone bed beneath it, and the pipe then carries it away. Holes-up is the most common mistake in a DIY french drain and it roughly halves the drain rate.
  • Wrap the entire trench in filter fabric — bottom, sides, and folded over the top before the topsoil goes back. Soil migrating into the stone is what silts a drain up permanently.
  • Slope at least 1% — an inch of fall for every 8 feet — toward a daylight outlet or a dry well. A level french drain is a trench full of standing water.
  • Stone is heavy. A 60 ft drain wants around 4 tons, which is a truck delivery rather than a trailer load. Have somewhere for it to be dumped close to the trench.

Common questions

How much gravel do I need for a french drain?

Multiply trench length, width and depth for the volume, take about 8% off for the pipe, and convert at roughly 105 lb per cubic foot. A 60 ft trench 12 in wide and 18 in deep needs about 4 tons of washed stone.

What kind of gravel goes in a french drain?

Washed #57 stone — clean, angular, roughly 3/4 in, with no fines. Never use crusher run or bank run gravel: the fines pack together and the drain silts up within a couple of years.

Should the pipe holes face up or down?

Down. Water enters the pipe from below through the stone bed and is then carried away. Holes-up means water has to fill the whole trench before it reaches the pipe, which halves the effective drain rate.

How deep should a french drain be?

Deep enough to sit below whatever you are protecting — usually 18 to 24 in for a yard drain and to the footing depth alongside a foundation. It also needs to reach an outlet lower than the drain bottom.

Do I need filter fabric?

Yes. Wrap the whole trench and overlap the fabric at the top before backfilling. Fabric keeps soil out of the stone. A french drain without it silts up from the outside in and cannot be cleaned.

How much slope does a french drain need?

At least 1%, or about 1 in of fall for every 8 ft of run, consistently toward the outlet. More is better. A drain with no fall holds water instead of moving it, and in freezing climates that is worse than no drain at all.

Related calculators