French Drain Pipe Calculator
Enter the length of your drain trench — straight run, perimeter, or diameter — to find out exactly how many rolls of pipe and dollars you’ll need.
Covers curves, corners and offcuts. 5–15% is normal.
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Ordering tips
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Coverage & waste
Material profile
For a 75 ft straight drain run using 4in perforated corrugated pipe with 10% waste, you need 1 roll (100 ft coil) covering the 82.5 ft required length. At $95 per roll, that’s about $95 in pipe material.
French drain pipe needed for common runs
Quantities include a 10% waste allowance for bends, connections, and trim at both ends of the trench.
| Drain run | Length with waste | Pipe type | Rolls needed |
|---|---|---|---|
| Downspout extension, 30 ft straight run | 33.0 ft | 4in perforated pipe | 1 roll |
| Yard drain, 50 ft straight run | 55.0 ft | 4in perforated pipe | 1 roll |
| Foundation perimeter drain, 75 ft straight run | 82.5 ft | 4in perforated pipe | 1 roll |
| Foundation loop, 40 × 30 ft perimeter | 154.0 ft | 4in perforated pipe | 2 rolls |
| Long backyard run, 100 ft straight run | 110.0 ft | 6in perforated pipe | 2 rolls |
| Extended slope drain, 150 ft straight run | 165.0 ft | 4in socked pipe | 2 rolls |
How to calculate french drain pipe you need
- Measure your drain run length. For a straight trench, measure end to end. For a perimeter drain around a foundation, add up all sides. For a circular catch loop, multiply diameter by π (≈3.1416).
- Add a waste allowance. Multiply by 1 plus your waste percentage — 10% covers trim at fittings, cleanouts, and connection overlaps.
- Divide by roll coverage. Divide by the linear feet one roll covers — standard perforated and socked pipe is sold in 100 ft coils.
- Round up to full rolls. You can’t buy a partial coil, so round the result up to the next whole roll, even if it leaves some leftover pipe.
- Add fittings and fabric separately. Budget for end caps, tees, couplers, and filter fabric or gravel wrap on top of the pipe itself — this calculator covers pipe only.
Worked example
Using the calculator’s defaults: a 75 ft straight drain run, 4in perforated corrugated pipe, 10% waste, $95 per 100 ft roll.
- Drain run length75 ft
- Length with 10% waste75 × 1.10 = 82.5 ft
- Coverage per roll100 ft
- Rolls needed (82.5 ÷ 100, rounded up)1 roll
- Roll cost (1 × $95)$95.00
- Total estimated cost$95.00
Choosing a french drain pipe type
Match the pipe to your soil conditions, expected water volume, and how much long-term maintenance you want to avoid.
- 4in perforated corrugated pipeStandard residential French drains — handles typical downspout and yard drainage at the lowest material cost.
- 6in perforated corrugated pipeHigh-flow drainage for larger sites, steep grades, or areas that see heavy seasonal runoff volume.
- 4in socked (fabric-wrapped) pipeSilty or fine-grained soil where bare perforated pipe would clog quickly — the fabric sock filters sediment before it reaches the perforations.
- Solid vs. perforated sectionsUse solid (non-perforated) pipe for the discharge run leading away from the collection area, and perforated pipe only where you want water to enter the drain.
- Gravel and fabric wrapRegardless of pipe type, wrap the trench in landscape fabric and backfill with washed drain rock to keep soil from migrating into the perforations over time.
Common mistakes
- Measuring trench area instead of drain run length.Pipe quantity follows the linear run of the trench, not its width or the excavated volume — those matter for gravel, not pipe.
- Skipping waste for fittings and connections.Tees, couplers, and cleanouts all consume extra length — build in at least 10% so you’re not short a few feet at the last connection.
- Choosing bare pipe in silty soil.Unsocked perforated pipe clogs faster in fine-grained soil — socked pipe or a separate fabric wrap keeps sediment out of the perforations.
- Ignoring pipe diameter for the water volume.4in pipe is fine for typical yard drainage, but high-flow sites (roof runoff, hillside seepage) need 6in pipe to avoid backups.
- Forgetting the outlet and slope.A French drain needs consistent fall (about 1% minimum) to a daylight outlet or dry well — pipe alone won’t move water without grade.
- Buying exact footage with no waste allowance.A single extra fitting or an unexpected bend around an obstacle can leave you short — always round up to the next full roll.
What this calculator assumes
Adjust your result if your project differs from these.
- Drain run length is measured along the actual trench path, not a simplified straight-line distance.
- A 10% waste allowance covers standard fittings, connections, and trim at both ends of the run.
- Perforated and socked pipe are both assumed to be sold in standard 100 ft coils.
- Perimeter drain length around a structure is calculated as the sum of all four sides.
- Circular catch-loop length is calculated as π × diameter (circumference).
- This calculator estimates pipe only — gravel backfill, fabric, fittings, and a catch basin or daylight outlet are priced separately.
Common questions
How much pipe do I need for a 75 ft French drain?
For a 75 ft straight run with 10% waste, you need 1 roll of 100 ft perforated pipe — the 82.5 ft required length fits within a single coil.
Do I need socked pipe or is bare perforated pipe fine?
Bare perforated pipe works in well-draining, sandy or gravelly soil. Socked pipe is recommended for silty or clay-heavy soil to reduce clogging.
What size pipe should I use for a French drain?
4in pipe handles most residential downspout and yard drainage. Step up to 6in for high-flow sites or steep hillside runoff.
How do I calculate pipe for a perimeter foundation drain?
Add up the length of all sides around the foundation to get the total run, then apply the same waste and roll-coverage formula.
How much waste should I add for French drain pipe?
10% is standard, covering fittings, cleanouts, and trim. Increase slightly for runs with several turns or tie-ins.
Does this calculator include gravel and fabric?
No — this tool estimates pipe quantity only. Gravel backfill and filter fabric should be calculated and priced separately.
What slope does a French drain pipe need?
A minimum of about 1% fall (1/8in per foot) is recommended so water moves reliably to the outlet instead of pooling in the trench.
Can I connect two rolls of pipe together?
Yes — standard couplers join sections of corrugated pipe; just add coupler cost and a small amount of extra waste for the overlap.
Where should a French drain discharge?
To a daylight outlet downhill, a dry well, or a sump pump pit — never to a spot that just relocates the water problem closer to the foundation.
Is 4in or 6in pipe more common for residential use?
4in is by far the most common choice for typical yard and foundation drainage; 6in is reserved for higher-volume or larger commercial sites.
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Project
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| Dimensions | — |
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Shopping list
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| Estimated total cost | — |
Notes
Estimate generated by materialcalculate.com. Confirm quantities with your supplier before ordering.