Last updated: 2026-06-18
Quick Answer
A standard 12" wide x 18" deep French drain needs about 0.056 cubic yards of 3/4" drainage gravel per linear foot after subtracting the pipe. A 50-foot run works out to roughly 2.8 cubic yards (about 4 tons) of gravel, 55 feet of 4" perforated pipe, and 250 sq ft of filter fabric with 10% waste. Installed, expect $12-$30 per linear foot in 2026. This calculator handles trench dimensions, pipe size, waste factor, and a full material and installed cost estimate.
Inputs you'll need
- Trench length (total linear feet of the drain run)
- Trench width (inches - 12" is typical)
- Trench depth (inches - 18" to 24" is typical)
- Perforated pipe size (4" for most homes, 6" for large areas)
- Waste percentage (10% is typical for gravel and pipe)
Buying gravel by the load? Cross-check the volume with our Gravel Calculator, and size the digging with the Excavation Calculator.
How to use this French drain calculator
- Enter the trench length in linear feet.
- Set the trench width and depth in inches (12" x 18" is standard).
- Pick your perforated pipe size - 4" covers most residential runs.
- Set your waste factor (10% is typical for gravel settling and pipe overage).
- Optionally enter your zip code or state for regional pricing adjustments.
Once you have your gravel and pipe takeoff, Try EstimationPro free to turn it into a professional proposal that follows up with the homeowner automatically so you win more of the bids you already send.
Total linear feet of drain run
12" is typical
18"-24" is typical
4" handles most residential runs; use 6" for large drainage areas.
10% typical for gravel and pipe overage
12,800+ estimates calculated this month
French Drain Estimate
Drainage Gravel
4.03
tons (2.88 cu yds, incl. 10% waste)
Perforated Pipe
55
linear ft (4" diameter)
Trench & Materials
Material Cost Estimate
Installed Cost (Excavation + Labor + Materials)
Installed range covers hand or machine excavation, gravel, pipe, fabric, and labor for a standard residential drain. Hauling spoil, hard digging through rock or roots, and connecting to a daylight outlet or dry well are extra.
French Drain Estimating Guide
Trench sizing, gravel tonnage, pipe selection, filter fabric, and installed cost for accurate drainage takeoffs.
What a French Drain Actually Needs
A French drain is a gravel-filled trench with a perforated pipe at the bottom that carries water away from a problem area. The gravel does the collecting, the pipe does the moving, and the filter fabric keeps soil from clogging the system. Get any one of those wrong and the drain fails within a couple of seasons.
- Trench: Typically 12" wide and 18"-24" deep for residential work. Wider or deeper for high-volume runoff or to reach below a footing.
- Perforated pipe: 4" diameter handles almost all residential drainage. Step up to 6" for long runs or large catchment areas.
- Drainage gravel: 3/4" washed stone is the standard. Avoid fines and crushed dust - they pack down and stop water from moving.
- Filter fabric: Non-woven geotextile wraps the trench (and sometimes the pipe) so dirt does not migrate into the gravel.
Slope matters as much as material. Aim for at least 1% fall (about 1 inch of drop every 8-10 feet) so gravity keeps water moving toward the outlet.
Key Takeaways
- 12" wide x 18"-24" deep is the standard residential trench
- 4" perforated pipe covers most homes; 6" for large areas
- Use 3/4" washed stone - never crushed fines that pack down
How Much Gravel a French Drain Takes
A 50-foot drain in a 12" x 18" trench needs roughly 2.8 cubic yards (about 4 tons) of drainage gravel after a 10% waste factor. The math is straightforward: trench volume in cubic feet, minus the space the pipe takes up, divided by 27 to get cubic yards.
- Trench volume: length (ft) x width (ft) x depth (ft) = cubic feet.
- Subtract the pipe: a 4" pipe displaces about 0.087 cubic feet per linear foot of trench.
- Convert to yards: divide cubic feet by 27.
- Convert to tons: drainage stone weighs about 1.4 tons per cubic yard, so multiply yards by 1.4 when ordering by weight.
Most suppliers sell drainage gravel by the ton. Order 10% extra so you do not stop mid-job for a half-yard short - a second delivery fee costs more than the overage.
Key Takeaways
- Trench cu ft = length x width x depth (all in feet)
- Drainage stone weighs ~1.4 tons per cubic yard
- Order 10% extra to avoid a second delivery fee
French Drain Cost: Materials vs Installed
Installed, a residential French drain runs $12 to $30 per linear foot in 2026 depending on depth, soil, and access. Materials alone are a fraction of that - the cost is in the digging and the labor.
- Drainage gravel: roughly $40-$55 per ton delivered.
- Perforated pipe: $0.70-$1.80 per linear foot for 4" corrugated.
- Filter fabric: about $0.20-$0.30 per square foot for non-woven geotextile.
- Labor + excavation: the biggest line item, especially in clay, rock, or tight backyards where a machine cannot reach.
Prices vary by region and by how hard the dig is. Always get local quotes and price a daylight outlet, pop-up emitter, or dry well separately - that connection is where a lot of estimates fall short.
Key Takeaways
- Installed cost is $12-$30 per linear foot in 2026
- Excavation and labor drive cost far more than materials
- Price the outlet (daylight, emitter, or dry well) separately
Common French Drain Estimating Mistakes
The two most common errors are ordering too little gravel and skipping the filter fabric. Both come back to haunt you - one stops the job, the other clogs the drain in a few years.
- Forgetting waste: gravel settles and spreads. Without a 10% buffer you will run short on a long run.
- No filter fabric: bare gravel silts up. Wrapping the trench is cheap insurance that doubles the drain's lifespan.
- Wrong stone: crushed fines or "drainage" bags with dust pack down and hold water instead of moving it.
- Flat trench: no slope means standing water. Confirm at least 1% fall before backfilling.
- Pipe holes up: perforations face down so water enters from the soil and the pipe fills from the bottom.
Measure the run, confirm the slope, and order gravel by the ton with a 10% buffer. That is 90% of a clean French drain estimate.
Key Takeaways
- Always add a 10% gravel waste factor
- Never skip filter fabric - it doubles drain lifespan
- Confirm at least 1% slope before backfilling
French drain quantity examples (3 test cases)
Use these to sanity-check your numbers. Gravel quantities include a 10% waste factor.
| Case | Trench | Expected |
|---|---|---|
| Short downspout drain | 20 ft, 12" wide x 12" deep, 4" pipe, 10% waste | ~0.74 cu yds (1.04 tons), 22 ft pipe, 80 sq ft fabric |
| Standard yard drain | 50 ft, 12" wide x 18" deep, 4" pipe, 10% waste | ~2.88 cu yds (4.03 tons), 55 ft pipe, 250 sq ft fabric |
| Deep curtain drain | 120 ft, 18" wide x 24" deep, 4" pipe, 10% waste | ~14.24 cu yds (19.94 tons), 132 ft pipe, 780 sq ft fabric |
Trench sizing and gravel at a glance
| Trench Size | Use Case | Gravel / Linear Ft | Pipe Size |
|---|---|---|---|
| 12" x 12" | Downspout / surface runoff | ~0.037 cu yds | 4" |
| 12" x 18" | Standard yard drain | ~0.056 cu yds | 4" |
| 12" x 24" | Wet yard / high water table | ~0.074 cu yds | 4" |
| 18" x 24" | Curtain drain / footing drain | ~0.111 cu yds | 4"-6" |
Gravel per linear foot shown before waste. Drainage stone weighs about 1.4 tons per cubic yard.
Common mistakes with French drain estimates
- Ordering gravel without waste. Stone settles and spreads as you backfill. Without a 10% buffer you stop the job for a half-yard short, and a second delivery fee costs more than the overage.
- Skipping filter fabric. Bare gravel silts up within a few seasons. Non-woven geotextile at $0.20-$0.30/sq ft is cheap insurance that roughly doubles the drain's lifespan.
- Using the wrong stone. Crushed fines and "drainage" bags with dust pack down and hold water. Use 3/4" washed stone so water actually moves.
- Forgetting the slope. A French drain needs at least 1% fall (1 inch per 8-10 feet). A flat trench leaves standing water and the system fails.
- Not pricing the outlet. The connection to daylight, a pop-up emitter, or a dry well is where a lot of estimates fall short. Price it as a separate line item.
From takeoff to a finished bid
I've been in the trades for 20+ years, and drainage work is one of those jobs where the estimate makes or breaks the margin. Counting gravel and pipe is just step one. You still have to price the dig, write it up, send it, and follow up before the homeowner calls someone else. EstimationPro handles the full workflow - estimate, proposal, automated follow-up, invoicing - so you spend less time on paperwork and more time in the trench. Try EstimationPro free.
How to Use This Calculator
Measure your trench length
Enter the total linear feet of the drain run from the problem area to the outlet. Long runs may need a 6" pipe.
Set trench width and depth
Most residential French drains are 12" wide and 18"-24" deep. Go deeper to reach below a footing or to handle heavy runoff.
Pick your perforated pipe size
A 4" perforated pipe handles almost all residential drainage. Step up to 6" for large catchment areas or long runs.
Add a waste factor
Set waste to 10% so gravel settling and pipe couplings do not leave you short mid-job. The calculator returns gravel in both cubic yards and tons.
French Drain Calculator Formulas
Trench Volume (cu ft) = Length × (Width ÷ 12) × (Depth ÷ 12)
Pipe Volume (cu ft) = π × (Pipe Dia ÷ 12 ÷ 2)² × Length
Gravel (cu yds) = (Trench Vol − Pipe Vol) ÷ 27 × (1 + Waste%)
Gravel (tons) = Gravel cu yds × 1.4
Pipe (linear ft) = Length × (1 + Waste%)
Filter Fabric (sq ft) = Length × ((Width + 2 × Depth + 12) ÷ 12)Where:
- Width / Depth
- = Trench dimensions in inches (12" wide × 18"-24" deep is standard residential)
- 1.4 tons / cu yd
- = Approximate weight of 3/4" washed drainage stone
- Waste%
- = Overage for gravel settling and pipe couplings (10% typical)
- +12" fabric
- = 12" overlap added so geotextile laps over the top of the gravel
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Frequently Asked Questions
How much gravel do I need for a French drain?
What size pipe should a French drain use?
How much does it cost to install a French drain?
Do I need filter fabric for a French drain?
How do contractors price a French drain job for a client?
How long does it take to estimate a French drain?
What slope does a French drain need?
Related Tools
- Gravel Calculator - Yards and tons of gravel for any project
- Excavation Calculator - Estimate digging volume and cost
- Drain Slope Calculator - Check fall and pipe slope
- Crusher Run Calculator - Base stone for driveways and trenches
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