50 ft yard drain, 4 in pipe
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The trench is 75 ft³. The pipe takes 4.4 ft³ of that, leaving 70.6 ft³. Ten percent waste makes 77.7 ft³, which is 2.88 yd³ or 4.03 tons. The fabric sheet is 12 + 2 × 18 + 12 = 60 in wide, 250 ft² in all.
French Drain Installation Cost Calculator: Gravel and Pipe
Calculator
Result
Order 2.88 yd³ of drainage stone, 5 lengths of pipe (50′ in all) and 250 ft² of filter fabric. It falls 6″ (1%), which meets the 1% minimum.
Gravel
2.88 yd³
4.03 tons at the density you set. Pipe volume already subtracted, waste added.
Fall
6″ over 50′
1% is 1 3/16″ every 10 ft. Ground slopes with the drain, so the depth stays the same.
Pipe
50′
5 × 10 ft sticks, before fittings and the outlet run.
Filter fabric
250 ft²
Sheet width 5′: trench width plus both sides plus overlap. Check the roll you can buy.
Sample cost
$319
$6.38 per ft. stone $181, pipe $75.00, fabric $62.50. Edit the prices. They are not a quote.
Trench
75 ft³ · 2.12 m³
Pipe takes 4.4 ft³ of that.
- Passes: Slope at least 1% (about 1″ per 8 ft): 1%
- Passes: Deepest point 18″, under 48″: deeper trenches can collapse
Type the trench size and your prices. This French drain calculator takes the pipe out of the gravel, then gives cubic yards, tons, filter fabric, pipe length and the fall, so you know how much gravel for a French drain to order before the truck is booked. Add a labor rate per foot and you have the French drain installation cost, materials plus labor.
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- Reviewed 15 October 2026
- Estimates only
Quick answer A 50 ft trench, 12 in wide and 18 in deep, with a 4 in pipe and 10% waste takes 2.88 yd³ of gravel (4.03 tons at 1.4 tons/yd³), 5 sticks of 10 ft pipe and 250 ft² of filter fabric.
How it works
A French drain with gravel and a perforated pipe is a long box with a cylinder in it. To calculate gravel for a French drain, take the trench as the box and subtract the pipe as a cylinder of the nominal diameter running the same length. That is the whole job of a French drain gravel calculator, and it works for any stone you choose, so a French drain rock calculator is the same tool. The gravel comes out in cubic yards and tons. Waste covers an uneven trench and stone that sinks into the soil.
Filter fabric is figured as a wrap: the bottom, both sides, and an overlap across the top that you can change. The sheet is trench width + 2 × depth + overlap wide, and as long as the trench.
Slope is a percent of the run. The total drop is length × slope ÷ 100, so 1% is 12 in over 100 ft, about 1 in every 8 ft, and the calculator flags anything under that. On ground that already slopes the right way, the trench can keep one depth. On level ground the bottom still has to fall, so the trench gets deeper toward the outlet, and the stone and fabric are figured at the average depth. That is why a long drain on flat ground can take a third more stone than the same drain on a slope, and why the outlet end can end up deep.
A French drain cost calculator multiplies each quantity by the price you enter: stone by the ton, pipe by the foot, fabric by the square foot, and labor by the foot if you add a rate. The total and the cost per foot are an estimate from your prices, not a quote. Digging, hauling the spoil and the outlet are the parts of a contractor's price that materials do not cover.
A patio on a well-drained base starts with the paver calculator. The roofing calculator gives the roof area that sends water to the drain, and the squaring calculator helps lay out straight, square trench lines.
Formula
V = gravel volume, L × W × D = trench (D is the average depth on level ground), r = pipe radius, w = waste %.
trench ft³ = length × width × depth (all in feet)
pipe ft³ = length × π × radius²
gravel ft³ = (trench − pipe) × (1 + waste/100)
gravel yd³ = gravel ft³ / 27
tons = gravel yd³ × density
fabric width = width + 2 × depth + overlap
pipe sticks = ceil( length / stick length )
drop = length × slope% / 100
level ground = trench depth at the outlet = start depth + drop
average depth = start depth + drop / 2 (used for stone and fabric)
cost = tons × price + pipe ft × price + fabric ft² × price + labor ft × rateWorked examples
80 ft, 24 in deep, 6 in pipe
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A longer, deeper trench with a bigger pipe: 160 ft³ of trench, 15.7 ft³ of pipe, 5.88 yd³ (8.23 tons) of gravel after waste, 8 sticks of pipe and 480 ft² of fabric. The pipe subtraction matters more here than on a 4 in line.
100 ft drain on level ground
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At 1% the pipe falls 12″ over 100 ft. The trench is 18 in deep at the high end, so on level ground it is 30″ deep at the outlet and 24″ on average. The gravel is 7.79 yd³ (10.91 tons), against 5.76 yd³ if the ground fell with the drain and the depth stayed at 18 in. At the sample prices the materials come to $791, or $7.91 a foot.
15 m, 300 × 450 mm, 100 mm pipe
Show the working
2.1 m³ of drainage stone (3.48 t) after 10% waste, 5 lengths of 3 m pipe and 22.5 m² of geotextile, which is a 1.5 m wide sheet. Ask the merchant for the bulk density of the stone they sell, because it varies.
How much gravel for a French drain?
Ballpark your order before you call the quarry. Each row is a trench 12 in wide and 18 in deep with a 4 in perforated pipe, 10% waste, 1.4 tons per cubic yard of stone and 12 in of fabric overlap, straight from the calculation above. Stone is sold by the ton, so check that column against your supplier's density.
| Drain length | Gravel (yd³) | Gravel (tons) | Filter fabric (ft²) | 10 ft pipe pieces |
|---|---|---|---|---|
| 25 ft | 1.44 | 2.01 | 125 | 3 |
| 50 ft | 2.88 | 4.03 | 250 | 5 |
| 75 ft | 4.32 | 6.04 | 375 | 8 |
| 100 ft | 5.76 | 8.06 | 500 | 10 |
| 150 ft | 8.63 | 12.09 | 750 | 15 |
French drain slope: fall and outlet depth by length
A drain with no fall is a long, expensive pond, so check this before you dig. The table assumes level ground and a trench 18 in deep at the high end, so it gets deeper toward the outlet. Use it as a French drain slope calculator: pick the length, read the drop at 1% or 2%, and make sure the outlet end is deep enough to take it.
| Drain length | Drop at 1% | Drop at 2% | Outlet depth at 1% | Gravel at 1% (yd³) |
|---|---|---|---|---|
| 25 ft | 3″ | 6″ | 21″ | 1.57 |
| 50 ft | 6″ | 12″ | 24″ | 3.39 |
| 100 ft | 12″ | 24″ | 30″ | 7.79 |
| 150 ft | 18″ | 36″ | 36″ | 13.22 |
French drain installation cost by length
French drain installation cost is the materials plus the digging, hauling and labor. The first table is the sample material cost from the calculator's prices ($45 a ton for stone, $1.50 a foot for pipe, $0.25 a square foot for fabric). The second adds labor at three example rates per foot, so you can see how the cost to install a French drain moves with a contractor's quote. Neither is a quote. Swap in your own prices, and add the labor rate to the materials per foot for an installed cost per foot.
| Drain length | Stone | Pipe | Fabric | Materials | Per foot |
|---|---|---|---|---|---|
| 25 ft | $90.65 | $37.50 | $31.25 | $159 | $6.38 |
| 50 ft | $181 | $75.00 | $62.50 | $319 | $6.38 |
| 100 ft | $363 | $150 | $125 | $638 | $6.38 |
| 150 ft | $544 | $225 | $188 | $956 | $6.38 |
| Drain length | Materials only | Labor $10/ft | Labor $20/ft | Labor $30/ft |
|---|---|---|---|---|
| 25 ft | $159 | $409 | $659 | $909 |
| 50 ft | $319 | $819 | $1,319 | $1,819 |
| 100 ft | $638 | $1,638 | $2,638 | $3,638 |
| 150 ft | $956 | $2,456 | $3,956 | $5,456 |
Code notes
Footing and foundation drains are covered by IRC Section R405, and where they may discharge is a local rule. A yard drain that daylights onto a neighbour, or into a sanitary sewer, is often not allowed. Keep the outlet at daylight, a dry well or a storm connection you have permission to use. The IRC text is in IRC 2021 Chapter 4, Foundations.
Use clean, open-graded stone such as #57 or 20 mm drainage stone, wrapped in filter fabric so soil does not fill the voids. Crusher run has fines that can clog the drain. Install the perforated pipe the way the manufacturer says. The fall should be at least about 1% (1 in per 8 ft); the calculator checks it and shows the drop. Call 811 (in the US) or your local utility locator before you dig.
The 1.4 tons/yd³ default is a mid-range figure for clean drainage stone. It is not a lab value, and suppliers quote anything from about 1.3 to 1.5. Type your yard's number if they print one.
Section numbers refer to IRC 2021 section numbers; England Approved Document K. Local amendments are common, so confirm with your building authority.
FAQ
Hover a question to read the answer. Click to keep it open.Tap a question to open it.
How many yards of gravel for a French drain?
Trench length × width × depth, minus the volume of the pipe, plus waste. A 50 ft trench, 12 in wide and 18 in deep, with a 4 in pipe and 10% waste, is just under 3 cubic yards, or about 4 tons at 1.4 tons per yard. A common yard drain is about 12 in wide and 18 to 24 in deep with a 4 in perforated pipe, and the outlet you are allowed to use sets the depth. Clean #57 stone is usually quoted at 1.3 to 1.5 tons per cubic yard, so use the figure your supplier gives you.
Why subtract the pipe?
The pipe takes up room you would otherwise fill with stone. It is a small amount on a 4 in pipe and a bigger one on a 6 or 8 in pipe. The calculator uses the nominal diameter, which is slightly smaller than the real outside diameter, so the gravel order runs a little high. That is the safe direction.
How much filter fabric do I need?
Enough to line the bottom and both sides and overlap across the top. The sheet is trench width + 2 × depth + overlap wide, usually with about 12 in of overlap, times the trench length. That is an area, not a roll width, so check the roll you can actually buy.
What slope does a French drain need?
At least about 1%, which is 1 inch of fall every 8 feet, or about 12 inches over 100 feet. The trench bottom should fall evenly toward the outlet. Too little fall lets water stand in the pipe. More is fine if the outlet can take the flow. Type the slope in and the calculator shows the total drop, and flags anything under 1%.
Does this design the drain?
No. It estimates materials for a trench you have already decided on, and checks the fall you enter. Where the water comes from, where it goes and whether you need a permit are site questions. Ask your building department or a drainage contractor if the problem is near a foundation.
How much does a French drain cost, and how much is a French drain per foot?
Type in your prices for stone, pipe and fabric and the calculator adds them up and divides by the length. At the sample prices a 100 ft drain is about $638 in materials, or $6.38 a foot. That is materials only. A contractor's price also covers digging, hauling and the outlet, so get written quotes for a real number.
What is the French drain installation cost?
Materials plus labor. Add a labor rate per foot in the calculator to see the installed total. At the sample material prices a 100 ft drain with labor at $20 a foot comes to about $2,638. The cost to install a French drain goes up with depth, rock or roots in the trench, a long run to the outlet and any permit, so use the rate from a quote, not this example.
How much gravel do I need for a 100 foot French drain?
A trench 12 inches wide and 18 inches deep with a 4 inch pipe takes about 5.8 cubic yards, or 8.1 tons, with 10% waste. Change the width, depth or pipe size in the calculator to match your trench. It also works as a drain rock calculator for any stone you can price by the ton.