Calculate exact washed gravel tonnage, cubic yards, pipe displacement volume, geotextile fabric wrap, and excavated soil haul-away for residential and commercial drainage trenches.
Set 0 for exposed gravel trench
~40% open voids for water flow
2.30 Cubic Yards • Net of 4" Pipe (-4.36 ft³) and 4" Soil Cap (-16.67 ft³)
Perforated pipe bedded in 3/4" stone, wrapped in non-woven filter geotextile.
62.2 cu ft
4.5 ft roll width
-4.4 cu ft offset
@ 1.3x loose swell
1/8" per ft (1% fall)
Delivered stone
A standard 4-inch perforated drainage pipe occupies 4.36 cubic feet per 50 linear feet. Failing to subtract pipe displacement causes homeowners and contractors to over-order aggregate by 5% to 10%, accumulating unusable driveway gravel piles and inflated freight costs.
Tightly compacted subgrade soil expands by 30% to 40% when excavated due to aeration and loss of natural cohesion. A trench with 3.0 cubic yards of neat footprint yields nearly 4.0 cubic yards of loose dirt. Our calculator prevents surprise dumpster overflow and site logistics bottlenecks.
Water requires gravity to flow. d trench dug flat collects stagnant water that eventually siltates and fails. The calculator auto-computes the exact minimum elevation drop needed (1% fall or 1/8" per linear foot) to ensure non-stagnant, self-scouring velocity.
Buying too-narrow filter fabric rolls leaves the top of the gravel open, allowing surface silt to infiltrate and permanently cement the drain. The tool computes the exact roll width required for a complete 360° burrito wrap plus a mandatory 12-inch top overlap seam.
Simultaneously offsets cylindrical pipe displacement and topsoil sod caps from gross trench volume to yield 100% accurate net gravel tonnage.
Calculates minimum fabric roll width ($2 \times \text{Gravel Depth} + \text{Width} + 12"$) and total linear roll footage to avoid mid-job fabric splices.
Computes both solid in-bank cubic volume and loose spoil cubic yards using clay and loam swell factors for dumpster and trailer planning.
Recommended dimensional guidelines and gravel standards for common residential and civil drainage scenarios:
| Drainage Application | Typical Width | Typical Depth | Pipe Diameter | Recommended Aggregate |
|---|---|---|---|---|
| Subsurface Lawn Drain | 10 - 12 inches | 18 - 24 inches | 4-inch perforated | 3/4" Washed Crushed Stone (#57) |
| Basement / Footing Drain | 12 - 18 inches | 24 - 36 inches | 4" rigid PVC SDR-35 | 3/4" to 1" Washed Angular Stone |
| Driveway Curtain Interceptor | 8 - 12 inches | 12 - 16 inches | 3" or 4" perforated | 1" to 1.5" Washed River Rock (exposed) |
| Retaining Wall Heel Drain | 12 inches | Wall base + 12" | 4-inch perforated | 3/4" Washed Crushed Stone |
Enter overall run length in feet, select trench width (standard 12 inches), and enter planned total trench depth in inches.
Choose 4-inch, 3-inch, 6-inch, or no pipe. The engine automatically deducts cylindrical pipe volume displacement from the gravel requirement.
Specify topsoil depth (typically 4-6 inches) if turf will grow over the trench, and select your quarry rock bulk density factor.
Review final net gravel tonnage, cubic yards, fabric roll width, excavated dirt swell volume, and minimum required elevation drop.
A French drain functions as a preferential subterranean flow path. Groundwater migrates along the path of least hydrodynamic resistance. Native compact clay soils have low hydraulic conductivity ($10^{-7}$ cm/s), whereas clean washed 3/4-inch crushed gravel has an extremely high hydraulic conductivity ($> 1.0$ cm/s). Water entering the gravel bed falls rapidly by gravity into the bottom zone where the perforated pipe resides.
A common DIY error is installing perforated pipe with the holes facing upward. Drain pipes must always be installed with perforations facing downward (at the 4 o'clock and 8 o'clock positions) seated upon a 2-inch to 3-inch bedding layer of washed stone. As the groundwater table rises from the bottom of the trench, water enters the holes from below and is conveyed away before the water level can rise to saturate surrounding foundations or lawn roots.
The non-woven needle-punched geotextile fabric (4 oz to 6 oz weight) is the biological shield of the system. Woven silt fences or garden weed barriers are completely inappropriate because their woven slit fibers rapidly blind over with microscopic clay platelets, sealing the trench into a bathtub. Non-woven fabric contains thousands of multi-directional felt pores that facilitate continuous hydraulic throughput while filtering out fine silt.
To calculate gravel, find the total trench volume (Length x Width x Depth in feet), subtract the volume displaced by the drainage pipe (pi * r^2 * Length), and subtract any topsoil cap volume. Divide net cubic feet by 27 to get cubic yards, then multiply by 1.4 tons/yd³ for standard 3/4-inch washed crushed stone. For example, a 50-foot trench that is 12 inches wide and 20 inches deep with a 4-inch pipe requires approximately 2.3 cubic yards or 3.2 tons of gravel.
A 4-inch drain pipe displaces approximately 0.087 cubic feet of volume per linear foot (or about 4.4 cubic feet per 50 feet). While water flows through the perforated pipe, gravel cannot occupy that physical space. Failing to subtract pipe displacement causes you to overbuy aggregate by 5% to 10%, wasting money and delivery charges.
The industry standard for French drains is 3/4-inch to 1-inch washed, crushed angular stone (AASHTO #57 crushed limestone or granite). Angular rocks interlock cleanly while maintaining 40% open void space for rapid subterranean water conveyance. Avoid rounded pea gravel (which shifts and clogs) and quarry process or crusher run (which contains rock dust that cements into an impermeable barrier).
A French drain requires a continuous minimum downhill slope of 1% (1 foot of vertical drop for every 100 linear feet of trench, or approximately 1/8 inch of drop per linear foot). A 2% slope (1/4 inch per foot) is preferred where topography permits. Gravitational flow ensures water moves swiftly to the daylight discharge point without pooling or depositing silt.
Non-woven needle-punched polypropylene filter fabric lines the bottom and sides of the trench, fully burrito-wrapping both the gravel bed and perforated pipe. It allows groundwater to enter freely while acting as a microscopic physical filter that prevents native clay and soil silt from migrating into the stone voids. Unwrapped drains inevitably clog and fail within 2 to 5 years.
Compact bank soil expands by 25% to 35% when dug up due to aeration and loss of natural compaction (the soil swell factor). A trench measuring 2.5 cubic yards of solid subgrade produces roughly 3.25 cubic yards of loose spoil dirt. Factor in disposal fees or plan garden berm distribution accordingly.
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