● Interactive 5-Layer French Drain Trench Blueprint
Gravel Calculator for French Drain: Tons, Cubic Yards, Pipe & Fabric
Tap any trench layer on the blueprint below to calculate washed drainage stone, pipe volume displacement, geotextile burrito wrap, and excavation spoils.
1. Trench Dimensions37.5 cu ft
Standard yard French drain is 12″ wide × 18″–24″ deep.
2. Drainage Stone Type
Always use washed stone free of limestone dust/fines.
3. Perforated Pipe & Config
Automatically subtracts pipe displacement from gravel.
4. Compaction / Settling Waste10% Buffer
0% (Exact)10% (Standard)20% (Sloped/Wide)
Interactive Trench Cross-Section Blueprint (Tap Any Layer)
Top CapGravel FillPerf PipeGeotextile Wrap
Active Trench Layer: 2. Main Washed Drainage Gravel EnvelopeClick below to customize this zone:
FRENCH DRAIN GRAVEL & MATERIAL ESTIMATENet Stone: 1.26 Cu Yds
Drainage Gravel Needed
1.64 Tons
1.26 Cu Yds • 66 Bags (50 lb)
Est. Material Budget
$395
Range: $335 – $465
Bulk Dump Delivery vs. 50-lb Retail Bags Savings:$215
About This Interactive Gravel Calculator for French Drain: Key Features
A French drain is only as effective as the washed aggregate envelope surrounding the pipe. Ordering unwashed road base with fine stone dust will seal up your trench like concrete, while forgetting to subtract the volume displaced by your 4-inch or 6-inch perforated pipe leaves extra piles of stone on your driveway. Our interactive gravel calculator for a French drain models all five physical zones of a professional subsurface drainage trench so homeowners and landscapers can calculate exact stone tonnage, cubic yards, 50-pound bags, geotextile fabric width, and soil haul-off volume.
1. Exact Pipe & Top-Cap Volume Displacement
Unlike basic rectangular trench calculators, our formula automatically subtracts both the top surface cap (2 to 4 inches of turf sod, mulch, or decorative border rock) and the cylindrical volume of single or dual perforated pipes—giving you true net gravel cubic yards and tons.
2. Interactive 5-Layer Trench Blueprint
Click directly on any structural horizon in the SVG cross-section—Surface Cap, Washed Drainage Gravel, Perforated Pipe Cradle, Non-Woven Geotextile Wrap, or Trench Excavation—to adjust stone density, pipe diameter, fabric overlap, and soil swell factors in real time.
3. Geotextile “Burrito Wrap” Width Formula
Automatically computes the exact roll width and square footage of non-woven filter fabric needed to line the bottom, both vertical trench walls, and overlap 12 inches across the top of the gravel envelope so surrounding soil never migrates into the stone.
How to Use the Gravel Calculator for a French Drain (Step-by-Step)
Step 1: Enter Your Trench Length, Width & DepthInput your total drain length in feet and your trench width and depth in inches (for example, 50 ft long × 12″ wide × 18″ deep). The tool immediately calculates total gross trench volume.
Step 2: Select Your Washed Drainage Stone & Pipe SizeChoose between Washed #57 Crushed Stone, 1.5″ Round River Rock, Pea Gravel, or 2″ Coarse Drain Rock, and select whether you are installing a single 4″ pipe, dual 4″ pipes, or a 6″ main line.
Step 3: Click the Blueprint Layers to Customize Cap & FabricTap Layer 1 (Surface Cap) to set whether gravel goes all the way to the surface (0″ cap) or sits beneath 2″ to 4″ of sod/mulch. Tap Layer 4 (Geotextile Wrap) to choose your filter fabric weight.
Step 4: Compare Bulk Delivery vs. 50-lb Bags & PrintReview your net gravel requirement in Tons, Cubic Yards, and 50-lb bags along with loose soil excavation volume. Click “Copy Material List” or “Print / PDF” to save your shopping sheet.
How Much Gravel Do You Need for a French Drain? (Rules of Thumb)
For a standard 50-foot French drain trench dug 12 inches wide by 18 inches deep with a 2-inch top cap of sod or mulch and a single 4-inch perforated pipe, the gross gravel zone is 12 inches wide by 16 inches deep (66.7 cubic feet). After subtracting 4.4 cubic feet displaced by the 4-inch pipe and adding a 10% settling/compaction buffer, you need approximately 68.5 cubic feet (2.54 cubic yards) for a 100-foot run, or 34.3 cubic feet (1.26 cubic yards) for a 50-foot run. Using washed #57 crushed stone (1.3 tons per cubic yard), a 50-foot trench requires roughly 1.64 tons of gravel (or 66 bags of 50-lb gravel).
What is the best gravel to use for a French drain?+
The best aggregate for a French drain is washed #57 crushed stone (3/4-inch to 1-inch angular stone) or 1.5-inch washed round river rock. Both provide 35% to 40% open void space for rapid water flow and will not wash through the slots in a perforated pipe. Never use crusher run, road base, or unwashed gravel containing stone dust/fines, as the fine particles will clog your geotextile fabric and block water infiltration.
How many bags of gravel do I need for a 50-foot French drain?+
A 50-foot French drain measuring 12 inches wide by 18 inches deep (with a 2-inch top cap and a 4-inch perforated pipe) requires approximately 1.26 cubic yards (1.64 tons or 3,280 lbs) of drainage stone. If you buy pre-bagged gravel in 50-pound bags (0.5 cubic feet per bag), you will need about 66 bags. Because 66 bags cost $330 to $400 and require heavy lifting, ordering 1.75 to 2 tons of bulk washed #57 stone from a local landscape supply yard is usually $150 to $220 cheaper.
How wide should geotextile fabric be for wrapping a French drain trench?+
To create a proper “burrito wrap” around your gravel envelope, add the trench width + (2 × trench depth) + trench width for top overlap. For example, a 12-inch wide by 18-inch deep trench requires 12″ + 18″ + 18″ + 12″ = 60 inches (5 feet) of fabric width so the fabric lines the bottom, comes up both sides, and overlaps across the top before you place your surface sod or mulch.
How much gravel should go under a French drain pipe?+
For a standard yard drainage trench collecting surface and subsurface water, pour a 1.5-inch to 2-inch bedding layer of washed gravel on top of the geotextile fabric before laying your perforated pipe (holes facing down at the 4 o’clock and 8 o’clock positions). This bedding cradle elevates the pipe into the clean stone zone and allows groundwater to enter smoothly from underneath.
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