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French Drain Gravel Calculator: Stone, Pipe & Fabric for Yards

Most French drain calculators stop at a cubic-yard number. This one is built for a yard install: it turns your trench size into a list you can take to the yard or the store — stone, pipe, fabric, the soil you'll dig out, and the turf to put back — and checks whether the run can actually reach an outlet. For the dig itself, how to install a yard French drain walks through it step by step.

Trench width
Trench depth
Perforated pipe

Your shopping list

For a 50-ft drain, 12" wide × 18" deep

  • #57 clean crushed stone

    Order in bulk — bagged would be dozens of bags. Includes a 10% settling allowance.

    2.2 yd³

    ≈ 3.1 tons

  • 4-inch perforated pipe

    Includes ~5% for connectors. Lay it holes-down.

    53 ft

    ≈ 6 × 10-ft sticks

  • Filter fabric (geotextile)

    A 6-ft-wide roll wraps the stone with overlap.

    6 ft × 53 ft

    ≈ 318 sq ft

  • Topsoil & sod to cap it

    Restores the top 4" back to lawn. Sod includes ~10% for trimming.

    0.62 yd³

    + 55 sq ft sod

  • Materials, planning range

    Stone, pipe, fabric, topsoil and sod at typical yard prices. Delivery, tool rental and hauling are extra. Not a quote.

    $240–$420

    vs. $10–$35 per ft installed

  • Soil to move or haul

    Loose spoil from the trench — plan where it goes before you dig.

    3.5 yd³

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How it goes together

Yard French drain cross-sectionCross-section of a yard French drain trench. From the bottom up: undisturbed soil, a bedding layer of number 57 clean crushed stone, a perforated pipe laid holes-down on the bedding, clean stone filling the trench, all burrito-wrapped in filter fabric against the soil, and topsoil and sod capping the top few inches back to lawn.Trench depthTrench widthSod + topsoil capFilter fabric#57 clean stonePerforated pipe(holes down)
Stone is wrapped in filter fabric so soil can't clog it, the pipe sits low with its holes facing down, and the top few inches go back to lawn.

What this doesn't tell you

These are planning quantities, not a design. They assume a straight, even trench and clean #57 stone — real trenches vary, stone yields differ by supplier, and the fall check reads a single end-to-end drop, not the dips in between. It can't confirm your outlet is legal to discharge to or that the soil below will take the water. Measure along the whole run and confirm the outlet before you order.

How to read your results

The shopping list is ordered the way you'll buy: the big items first, the easy-to- forget ones last.

  • Stone in yards and tons. Yards is how bulk stone is priced and hauled; tons is how it's weighed at the quarry. Once you're past about a cubic yard, bulk delivery beats bagged — the tool says which side of that line you're on.
  • Pipe in sticks. Perforated pipe is sold in 10-foot sticks (and 100-foot coils); the count includes about 5% extra for connectors and offcuts.
  • Fabric as a roll. The figure is the roll width that will wrap all the way around the stone with overlap, times the length you need — not just a strip over the top.
  • Spoil to move. Excavated soil swells by about a quarter once it's loose. Knowing the volume up front means you decide where it goes before it's a pile on the lawn.

The formula — check it yourself

Gravel volume is just the trench, minus the space the pipe takes up:

cubic yards = (length ft × width ft × depth ft − pipe volume) ÷ 27

Convert width and depth from inches to feet first (divide by 12). Multiply the three dimensions for cubic feet, subtract the pipe, and divide by 27 for cubic yards. Multiply cubic yards by about 1.4 to get tons of #57 stone, and add roughly 10% so a delivery isn't short after the stone settles. When you cap the trench with sod, the tool holds back the top 4 inches for topsoil instead of filling it with stone.

Gravel: what to buy

Ask for #57 stone — clean, washed, angular ¾-inch crushed rock. " Clean" means the fines have been screened out, so the stone holds open voids for water instead of packing tight. Skip pea gravel (too round, shifts and silts), and skip crusher run and recycled concrete (full of fines that clog). If your yard supplier lists #67 or a local drainage-rock equivalent, those work too — the point is clean and angular.

Standard trench sizes

UseWidthDepthPipe
Shallow lawn / surface runoff6"12"4"
Typical yard French drain12"18"4"
Wet yard / higher water table12"24"4"
Long run / heavy flow12"24"6"

Will it reach an outlet?

A French drain only works if the water has somewhere lower to go. Tick check the fall to my outlet and enter how much lower the far end is, and the tool does two things generic calculators skip: it confirms the grade clears the 1% minimum, and it tells you whether the pipe can actually surface to daylight or whether it'll still be underground at the low end. If it can't daylight, the water needs storage instead — a dry well or a pop-up emitter. To measure the fall precisely, use the yard slope calculator, and to check whether 4-inch or 6-inch pipe can actually carry the water, the yard French drain sizing calculator.

From materials to cost

This calculator stops at quantities on purpose: stone and labour prices swing too much by region to quote honestly. For planning ranges — what a yard French drain typically runs per foot installed versus done yourself, and what moves the number — see yard French drain cost, or price a whole plan with the yard drainage cost calculator.

Frequently asked questions

How much gravel do I need for a French drain?
The stone you order is the trench volume minus the pipe: length × width × depth (all in feet) ÷ 27 = cubic yards, then about ×1.4 for tons of #57 clean stone, plus roughly 10% for settling. A 50-foot trench 12 inches wide and 18 inches deep, with stone all the way to the surface, works out to about 2.9 cubic yards — roughly 4 tons — once the pipe volume and settling are accounted for.
How much gravel do I need for a 100 ft French drain?
For a typical yard trench 12 inches wide and 18 inches deep with 4-inch pipe and a 10% settling allowance, about 5.8 cubic yards — roughly 8 tons of #57 stone — if the stone runs to the surface. Cap it with 4 inches of topsoil and sod instead and it drops to about 4.4 cubic yards, roughly 6 tons. A narrow 6 × 12-inch surface drain needs only about 1.7 cubic yards; a 12 × 24-inch drain for a wet yard about 7.8. At these volumes, bulk delivery is far cheaper than bags.
Can you use 3/4 gravel for a French drain? What size is best?
Yes — ¾-inch clean, angular crushed stone (sold as #57) is the standard choice. Its irregular faces lock together and leave open voids for water to move through. Don't use pea gravel: the round stones shift and pack down, and the fine grades silt up and choke the flow. Avoid crusher run and recycled concrete too — they contain fines that clog.
How deep and wide should the trench be?
Most yard French drains run 6 to 12 inches wide and 12 to 24 inches deep. Go deeper where the water table is higher or you're intercepting flow from uphill; a shallow surface drain can be as little as 12 inches deep. Whatever the depth, the trench still needs about 1% fall along its length to drain.
Should you put gravel under a French drain pipe?
Yes. Lay a bed of 2 to 3 inches of stone along the bottom of the trench before the pipe goes in, keeping the fall you set. The bed lets water reach the pipe from below and keeps the pipe off the soil, where silt would settle into it. Then surround and cover the pipe with more stone before the fabric is folded over.
Do I need filter fabric, and which way does it go?
In any soil with silt or clay, yes — without it, fines wash into the stone and clog the drain within a few years. Line the trench and 'burrito-wrap' the stone: fabric against the soil on the bottom and both sides, folded over the top before the cap. A fabric-sock pipe helps but is not a substitute for wrapping the stone.
Should the pipe holes face up or down?
Down. It's counterintuitive, but water enters the pipe from below as the water table rises into the stone, so holes-down lets it in at the lowest point and lets the pipe drain completely between storms. Holes-up leaves standing water in the bottom of the pipe, where silt collects.
How much slope does a French drain need?
About 1% — roughly ⅛ inch of fall per foot, or 1¼ inches per 10 feet — is the practical minimum for gravity flow. Below that, water sits in the pipe and it silts up. Tick 'check the fall to my outlet' above, or use the yard slope calculator to confirm your run has enough drop.
What will the gravel and installation cost?
This tool gives quantities, not prices, because stone and labour rates vary too much by region to quote honestly. As a rough planning figure, #57 stone runs on the order of $25–$60 a ton delivered in many areas — multiply that by the tonnage above for a materials ballpark. Treat it as a starting point for comparing supplier quotes, not an installed-cost figure.

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