Pricing a Drainage Job by the Foot: A Sanity Check
Divide the 148-foot French drain job by its length and you get $88.72 a foot — a number that's exactly right about that one yard and misleading everywhere else.
A 148-foot French drain, priced line by line, came to $13,130. Divide that by 148 and you get $88.72 a foot.
That number is real. It's also almost useless on the next job, and the reason is that nothing in the $13,130 scaled with length except the pipe, the fabric and the stone. The mobilization didn't. The restoration didn't. The two hours of hand digging around a gas line didn't.
Per-foot pricing isn't wrong. It's just in the wrong place in the sequence. It belongs at the end of your estimate as a check, not at the start as a method.
$88.72 a foot describes one yard, not a price list
Go back through the full breakdown of that 148-foot job and look at what's actually in the number. Materials, machine time, crew hours, spoil haul-off, restoration, overhead and margin. Some of those buckets multiply when the run gets longer. Most of them don't.
Mobilization is the obvious one. Loading the mini-ex, driving out, unloading, staging, loading back up at the end — that's the same half-day whether the trench is 60 feet or 200. Spread across 148 feet it's some number per foot. Spread across 60 feet it's two and a half times that number per foot.
Which is why short jobs look expensive per foot and long jobs look cheap, and why quoting the next 60-footer at $88.72 a foot means you just donated the difference.
The per-foot figure is an output. Treat it like one.
Depth moves the number faster than length does
Here's arithmetic you can do in the truck. A trench 12 inches wide and 24 inches deep has a cross-section of 2 square feet. Over 148 feet that's 296 cubic feet of spoil, or 10.96 cubic yards.
Take the same run to 36 inches deep. Cross-section is 3 square feet, so 444 cubic feet, or 16.44 cubic yards. Same length, same pipe, same fabric — and 50 percent more dirt out and roughly 50 percent more stone in.
Stone is usually the largest single material line on a French drain. If depth moves it by half, and depth isn't in your per-foot number, the per-foot number is fiction. A 148-foot run at 24 inches and a 148-foot run at 36 inches are not the same job and shouldn't carry the same price.
There's also a hard break point that has nothing to do with arithmetic. At five feet of depth, a trench needs a protective system — sloping, shoring or a box. That's not a percentage increase on your per-foot rate. That's a different job with different equipment and a different crew size, and if you quoted it off a per-foot instinct you've already lost.
Spoil is the quiet part. The extra 5.5 cubic yards from going a foot deeper swells when you dig it — loose dirt takes up noticeably more room than bank dirt. If you're hauling off rather than spreading on site, that's another trailer load, and trailer loads come in whole numbers.
Access and restoration are where the shortcut bleeds
Two sites, same run, same depth. On the first, you back the mini-ex down the side yard. On the second there's a 34-inch gate, a deck on one side and a retaining wall on the other, and everything moves by wheelbarrow.
Run the barrow math on that 10.96 cubic yards. A contractor barrow carries roughly six cubic feet heaped, so 296 cubic feet of spoil is about 49 trips out. Then the stone goes back the other way — call it another 45 trips in. Ninety-plus round trips down a side yard, plus the hand excavation itself.
Don't take my minutes-per-trip. Take your own. Next tight-access job, dig ten feet by hand and time it. Ten feet at 12 by 24 inches is 20 cubic feet, or 0.74 cubic yards. Whatever that took your crew, multiply by 14.8 and you have the hand-dig number for a 148-foot run in that soil. Do it once and you'll never guess again.
Restoration does the same thing from the other end, and it's cleaner to calculate. Say the disturbed strip is three feet wide. That's 444 square feet over 148 feet of trench — exactly three square feet of restoration per foot of drain.
So your restoration cost per foot is three times your installed sod price per square foot. Installed sod runs anywhere from under a dollar to well over two dollars a square foot depending on your market, your supplier and whether you're prepping or just laying. At the low end that's under $3 a foot of drain. At the high end it's over $7. Same trench, same pipe, and the per-foot number moved by four dollars before you touched anything underground.
Then there's the stuff that isn't per-foot at all: sawcutting and patching a concrete driveway, pulling and resetting pavers, rerouting around a mature root flare, working around irrigation you have to repair. Those are lump items. Smearing them across the length of the run is how a $2,400 concrete patch turns into $16 a foot that you forget to charge on the next job that doesn't have one.
| Variable | What changes on a 148-ft run | Effect on $/ft | How you catch it on site |
|---|---|---|---|
| Depth 24 in to 36 in | 10.96 cu yd of spoil becomes 16.44; stone up about half | Up, and materials-heavy | Shoot grade at both ends before you quote |
| Depth past 60 in | Protective system required; different crew and equipment | Not a percentage — a different job | Outfall elevation vs. inlet elevation |
| Machine to wheelbarrow | ~90 barrow round trips plus hand excavation | Up sharply, labor-heavy | Measure the narrowest gate and the slope |
| Spoil hauled vs. spread | Two to three loose yards per trailer load | Up in whole loads, not per foot | Ask where spoil can go before you leave |
| Sod restoration | 444 sq ft at 3 sq ft per foot of trench | 3 × your installed sod price, per foot | Walk the strip and note what it crosses |
| Hard surface crossing | Sawcut, removal, patch, cure time | Lump sum — keep it out of $/ft | Count crossings on the walk |
Build your band from your own last eight jobs
The useful per-foot number isn't one you read somewhere. It's the one your own closed jobs produce.
Pull your last eight drainage jobs of roughly the same type — say, French drain with a daylight outfall, no hard surface crossings. For each one, divide the final contract price by installed feet. Write the eight numbers down in order.
- Find the median. That's your center.
- Find the spread. If every job sits within roughly 10 to 15 percent of the median, the median is a usable check number for that job type.
- For every job outside the band, write down the one thing that put it there. Rock. A 200-foot haul from the truck. Forty feet at four feet deep. Full sod replacement on a manicured lawn.
- That list of reasons is worth more than the median. It's your pre-quote checklist.
- Do it separately for each job type. Surface drains, downspout tie-ins and full French drains don't share a band.
If the spread is wider than about 25 percent, per-foot isn't a checking tool for you yet — your jobs vary too much. That's not a failure. It usually means you work a range of soils or a range of neighborhoods, and the answer is line items, not averages.
What the site visit has to settle before per-foot means anything
Depth is the variable that moves the most money, and depth isn't a choice. It falls out of the diagnosis — where the water's coming from, where it can go, and what fall you have between the two.
That's why the walk comes first. A repeatable diagnostic on the first visit tells you the source, and the source tells you the depth, the length and whether one trench solves it or you need a second run. Quote the per-foot instinct before the diagnosis and you're pricing a job you haven't identified.
Once you know the depth and the route, the bid is mechanical. Every bucket gets a line: excavation, pipe, fabric, stone, outfall structure, spoil disposal, restoration, mobilization, overhead, margin. The line-item breakdown of a drainage estimate covers what belongs on each line and the four that contractors leave off until the job is already underwater.
Build the estimate that way and the per-foot number appears at the bottom by itself.
Run the check last, and know what it can't tell you
Your line items total up. Now divide by installed feet and look at the result against your band.
If it lands inside, send it. If it lands 20 percent low, something's missing — nine times out of ten it's restoration, spoil haul-off or the outfall structure. If it lands 30 percent high, either the site earned it, in which case the proposal needs to say plainly why this yard costs more than the neighbor's, or you've double-counted a bucket. Either way you found it before the homeowner did.
One honest limit. The check only compares your bid to your other bids. It says nothing about whether those jobs actually made money, because contract price isn't profit. To close that loop you need actual hours and actual material against the budget — job costing — and ScapesHQ doesn't do job costing. It isn't built and I'm not going to imply otherwise. A spreadsheet with columns for bid hours, actual hours, bid material and actual material, filled in the Friday after each job closes, will get you there.
Do that for a season and your band stops being a record of what you charged and starts being a record of what worked. That's the version worth checking against.
FAQ
What's a fair price per linear foot for a French drain?
It depends far more on depth, soil, access and restoration than on length, so any single figure you find online is describing someone else's yard. The honest answer is to divide your own last eight comparable jobs by their installed footage and use the median as a check. If those eight numbers spread more than about 25 percent, per-foot isn't reliable for your mix of work and you should bid line by line.
Why do short drainage runs cost more per foot than long ones?
Because mobilization, diagnosis, outfall construction and setup cost roughly the same regardless of length. Spread a fixed half-day of loading, driving and staging across 60 feet and the per-foot share is two and a half times what it is across 148 feet. That's the single most common way per-foot quoting loses money on small jobs.
How much does trench depth change the cost of a drain?
Cross-section scales directly with depth. A 12-inch-wide trench at 24 inches deep is 2 square feet of cross-section; at 36 inches it's 3 square feet, so a 148-foot run goes from 10.96 to 16.44 cubic yards of spoil and the stone goes up by roughly the same proportion. Past five feet of depth you also need a protective system, which changes the crew and equipment entirely.
Should restoration be included in a per-foot drainage price?
Only if you calculate it. If the disturbed strip is three feet wide, you're restoring three square feet for every foot of trench, so your restoration cost per foot is three times your installed sod price per square foot. Since installed sod varies widely by market and by whether you're prepping the soil, that alone can move your per-foot number by several dollars.
Can I use a per-foot rate to give a price over the phone?
You can give a range if you say clearly what it assumes — typical depth, machine access, and standard restoration — and that the real number comes after the site visit. What you should not do is commit to a figure before you know the outfall elevation and the gate width, because those two facts control most of the cost variance.
The short version
Per-foot pricing is an output, not a method. Bid the job line by line, then divide the total by installed feet and compare it to the band your own last eight comparable jobs produced — if it lands 20 percent low, you've probably left off restoration, spoil haul-off or the outfall. Depth, access and restoration move the number more than length does, and mobilization is why short runs always look expensive per foot.
Book a walkthrough and we'll divide a few of your own recent jobs by their footage and see how wide your band actually is.