Clean, washed crushed stone sold as #57 is a common French-drain option to ask about, not a universal specification. GoodGravel recommends #57, and the Florida drainage contractor StructureSmart recommends washed angular stone for its residential work.1,2 But NDS’s general installation guide allows a broader range, including pea gravel and river rock.3 Confirm the aggregate, filter and pipe detail for your soil and drainage design before buying.
Quick answer: choose the assembly, not just the stone name
- Start with the stone gradation and cleanliness required by the chosen pipe/filter design. Washed, screened stone is a supplier description to verify, not proof of compliance.
- Ask for the actual gradation and bulk density of the load. A #57 label or “drainage rock” name alone does not define every particle size or its weight.
- Select a drainage filter compatible with soil and the assembly. Generic weed barrier is not automatically a drainage filter.
- Confirm a suitable outlet, elevation, cover and safe excavation plan. Gravel choice alone cannot make an unsuitable layout work.
What the sources agree on, and where they differ
| Material | What our sources say | What to check |
|---|---|---|
| Washed angular crushed stone / #57 | GoodGravel and StructureSmart favor it for French drains. | Exact gradation, fines and the pipe/filter design. |
| Larger washed stone | StructureSmart suggests it for some heavy-flow applications; this is contractor guidance. | Do not infer hydraulic capacity or soil-filter compatibility from size alone. |
| Pea gravel | StructureSmart cautions against primary use around pipe in its Florida sandy-soil context; NDS includes it in a broader aggregate range. | Product and site detail. Not categorically ruled out by all sources. |
| River rock | StructureSmart favors it for surface channels rather than buried-pipe bedding; NDS includes larger river rock in its general guide. | Intended location and assembly. A surface-channel recommendation is not pipe-bedding approval. |
| Unwashed or fines-bearing mixes | StructureSmart warns against dust/fines around drain pipe. | Actual fines content and design requirements; do not substitute road base just because it is stone. |
These statements come from a gravel information site, a drainage contractor and a manufacturer’s general guide, not a single code or engineered detail. StructureSmart explicitly discusses Florida sandy soils.2 NDS says aggregate can range from pea gravel to river rock and mentions smaller pieces near the pipe and larger ones near the surface.3 That is a source disagreement, not evidence that one material is best everywhere.
Why cleanliness and filter compatibility matter
StructureSmart describes washed stone as removing dust, sand and clay from crushing and handling, and warns that fines can accumulate around pipe.2 NDS describes surrounding fabric as helping prevent dirt from mixing with the gravel while allowing water to pass.3 Read these as guidance on the whole assembly. A clean stone delivery does not remove the need to handle surrounding soil correctly.
We do not give a universal void-space percentage or lifespan here. Source claims such as “40% voids” or a fixed number of years do not establish the value for your actual gradation, placement, soil or filter. Likewise, a larger stone size is not a substitute for checking the pipe openings, filter and drainage capacity.
Stone numbers are not a complete product specification
The reviewed sources even give different simplified sizes for #4: GoodGravel calls it 1 to 1.5 inches in one section, while StructureSmart uses 1.5 to 2 inches.1,2 Ask the supplier for the gradation instead of translating the name into one guaranteed size. Our crushed-stone size chart helps interpret labels, but a source’s shorthand is not the supplier’s sieve specification.
How much drainage stone to order
Net gravel (cu yd) = (stone-envelope volume – pipe displacement) / 27. Use dimensions in feet for cubic-foot volume. The depth is the stone zone, not total excavation if soil or sod occupies the top. Pipe displacement depends on actual outside diameter/profile; a nominal 4-inch cylinder is an approximation. Apply a separately chosen quantity allowance, then check delivery increments with the supplier.
Short tons = cubic yards × supplier pounds per cubic yard / 2,000. Do not assume 1.4 short tons per cubic yard is the density of every washed drain stone. GoodGravel’s 0.055 tons per foot for a 12-by-12-inch trench implies 1.485 tons per cubic yard for the full envelope, before pipe displacement.1 That is its planning model, not a measurement of your supplier load. It also does not replace a pipe/cover-aware takeoff.
Example quantities with a nominal 4-inch pipe model
This calculated table uses a 50-foot, 12-inch-wide stone envelope, a 4-inch smooth-cylinder displacement model and 10% example allowance. These are not recommended trench depths or a universal allowance. No soil cover is included in the stone depth.
| Stone depth | Net gravel | With 10% example allowance |
|---|---|---|
| 12 in | 1.690 cu yd | 1.859 cu yd |
| 14 in | 1.999 cu yd | 2.199 cu yd |
| 18 in | 2.616 cu yd | 2.878 cu yd |
| 24 in | 3.542 cu yd | 3.896 cu yd |
Three checked quantity examples
1. 50-foot run, 12 × 12-inch stone envelope
Envelope: 50.000000 cu ft. Approximate pipe displacement: 4.363323 cu ft. Net gravel: (50.000000 – 4.363323) / 27 = 1.690247 cu yd. With 10% example quantity allowance: 1.859272 cu yd. Convert that allowance-inclusive amount to weight only after obtaining the supplier’s density. These examples calculate quantities, not drainage performance.
2. 30-foot run, 12 × 18-inch stone envelope
Envelope: 45.000000 cu ft. Approximate pipe displacement: 2.617994 cu ft. Net gravel: (45.000000 – 2.617994) / 27 = 1.569704 cu yd. With 10% example quantity allowance: 1.726674 cu yd. Convert that allowance-inclusive amount to weight only after obtaining the supplier’s density. These examples calculate quantities, not drainage performance.
3. 80-foot run, 18 × 24-inch stone envelope
Envelope: 240.000000 cu ft. Approximate pipe displacement: 6.981317 cu ft. Net gravel: (240.000000 – 6.981317) / 27 = 8.630322 cu yd. With 5% example quantity allowance: 9.061838 cu yd. Convert that allowance-inclusive amount to weight only after obtaining the supplier’s density. These examples calculate quantities, not drainage performance.
Fabric and safe layout are separate checks
The French drain calculator estimates a full rectangular filter wrap using both the bottom and top widths, two sides and our 12-inch closure-overlap model. Roll width, end closures and seams still need checking against the chosen filter instructions. Pipe size, slope, cover and outlet must follow the actual design; a quantity estimate cannot approve them.
Do not excavate beside footings or retaining walls using these example dimensions. Contact 811 and follow the state’s marking, response and safe-digging requirements, including private-line checks when needed. For persistent water problems or uncertain structure, outlet or soil conditions, get a qualified drainage assessment.
FAQ
Can I use pea gravel or river rock?
Not a universal yes or no. The reviewed contractor discourages some buried-pipe uses, but NDS’s general guide includes these materials. Follow the selected pipe/filter assembly and site design rather than treating one source’s preference as a nationwide prohibition.
Is #57 always 3/4-inch stone?
That is common supplier shorthand, not a complete gradation. A named grade contains a range of particle sizes. Ask what the actual supplier product contains and whether it meets the design.
Do I need washed stone?
Our contractor source favors washed stone to limit built-in fines. Confirm cleanliness and gradation required by your actual drain detail. A “washed” label alone does not check filter compatibility, capacity or safe installation.
Can I use 1.4 tons per yard for ordering?
Only if your supplier confirms that density for the exact material and moisture basis. Otherwise use cubic yards for quantity planning and get the supplier’s weight conversion. No universal density is asserted here.
Related tools and guides
French-drain gravel quantity guide | French drain calculator | Gravel calculator | Pea gravel versus crushed stone
Sources
- GoodGravel: Drainage Gravel Guide (gravel information site; material preferences and a length-based planning quantity)
- StructureSmart: Drainage Rock Guide (Florida drainage contractor; washed stone and site-context material cautions)
- NDS: French Drain Installation Guide (manufacturer general guide; broader aggregate range, fabric and layout)