French Drain Gravel: Best Types, Sizes, and How Much to Buy

For most residential French drains, use washed, angular 3/4-inch crushed stone — sold at quarries and suppliers as #57 stone. It drains fast, resists compaction, and stays open for decades when paired with the right filter fabric. A standard 50-ft trench at 12 inches wide and 18 inches deep needs roughly 2.78 cubic yards of stone before any buffer.

Here’s the short version before you dig in:

• Best material: Washed #57 crushed stone (3/4-inch angular)
• Trench size (typical residential): 12–18 inches wide, 18–24 inches deep
• Stone under pipe: 2 inches minimum
• Stone above pipe: 6 inches minimum
• Minimum slope: 1% (1 inch of drop per 8 feet of run)
• Order buffer: Add 10% to your calculated volume

Pro Tip: Never order by eyeballing the trench. Showing up with too little stone mid-project means a second delivery charge and a half-finished drain.

Key Takeaways

Table of Contents

• What gravel works best for a French drain?
• How to calculate how much gravel you need
• What trench dimensions and pipe placement should you use?
• Why geotextile fabric and the burrito-wrap method matter
• Common mistakes that cause French drains to fail
• How to buy and order gravel for your French drain
• A practical note on planning your material order
• Olearydevelopmentgroup delivers the right gravel, on time, to your site
• Sources
• FAQ

What gravel works best for a French drain?

The standard specification for residential French drains calls for open-graded, angular, washed crushed stone in the 3/4-inch range. “Open-graded” means the aggregate has a narrow size range with minimal fines, which preserves void space between particles. Angular edges from the crushing process lock particles together without compacting, so water moves through freely year after year.

Why #57 stone is the default choice

ASTM #57 gradation covers particles from 3/4 inch down to about 3/8 inch, with very little material passing a No. 4 sieve. That size range hits a practical sweet spot: large enough to maintain permeability, small enough to stay in place inside a fabric-wrapped trench. According to StructureSmart’s drainage rock guide, angular washed stone prevents compaction and maintains voids, while rounded or fine-laden aggregates like pea gravel and crusher run compact and clog a drain within a few years.

Acceptable alternatives for specific conditions

• #67 stone (3/4" to 3/8"): Slightly finer than #57; works in moderate-flow residential applications where your supplier doesn’t stock #57.
• #4 stone (1.5" to 3/4"): Coarser gradation suited to high-flow areas, deep trenches, or commercial runs where you need maximum void space.
• 1-inch septic rock: A common regional substitute in Texas and the Southeast; functions similarly to #57 and is often available locally. You can see one-inch septic rock specs as an example of what suppliers stock.

What to avoid

Pea gravel is smooth and rounded. It looks clean, but its rounded shape means particles roll past each other and compact under load. Crusher run contains fines by design — it’s made to compact, which is exactly what you don’t want in a drainage application. River rock can work in surface-level decorative channels but lacks the angular interlock needed for a buried drain envelope.

Pro Tip: When you call a supplier, ask specifically for “washed #57 crushed stone” and request a sieve analysis or a photo of the material. If the sample looks dusty or the fines coat your hand, reject it. Clean stone should look almost white or gray with no visible dust.

How to calculate how much gravel you need

The formula is straightforward. Every step below uses feet and cubic feet, then converts to cubic yards for ordering.

Step-by-step calculation

1. Measure your trench: Length (ft) × Width (ft) × Depth (ft) = total trench volume in cubic feet.
2. Subtract pipe displacement: A standard 4-inch perforated pipe displaces approximately 0.087 cubic feet per linear foot. Multiply that by your trench length.
3. Convert to cubic yards: Divide the net cubic feet by 27.
4. Add 10% buffer: Multiply your cubic yard figure by 1.10 to account for settling, uneven trench walls, and spillage.

Worked example: 50-ft trench at 12" × 18"

The French drain calculator at YardCalcApp confirms a 50-ft × 12-in × 18-in trench at approximately 2.78 cubic yards before the buffer, which aligns closely with this manual calculation. Round up to the nearest quarter yard when placing your order.

Converting cubic yards to tons

Quarries sell stone by weight, not volume. #57 crushed stone averages approximately 1.4 tons per cubic yard, per the remodelcalculators French drain guide. For the example above: 2.88 cu yd × 1.4 = 4.03 tons. Always confirm the density conversion with your specific supplier before finalizing the order, since local stone types vary.

Pro Tip: A standard 12-in × 18-in trench uses roughly over one cubic foot of stone per linear foot before pipe displacement. That quick-reference number lets you estimate any length in seconds: 100 ft of trench ≈ 140 cu ft ≈ 5.2 cu yd before buffer.

What trench dimensions and pipe placement should you use?

Standard residential trench dimensions

LSU AgCenter’s installation guide recommends a trench width of 12–18 inches and a depth of 18–24 inches for most residential French drains. Narrower trenches (under 10 inches) restrict stone volume and reduce the system’s ability to handle peak flow. Deeper trenches are sometimes needed to get below a foundation footing or to intercept groundwater at the right elevation.

Pipe placement and stone layering

Follow this sequence from the bottom of the trench up:

1. Lay 2 inches of #57 stone as a bedding layer before the pipe goes in.
2. Set the 4-inch perforated pipe on the bedding stone with holes facing down at the 4 and 8 o’clock positions.
3. Cover the pipe with at least 6 inches of stone above the top of the pipe for foundation drain applications.
4. Fold the geotextile fabric over the stone (see the next section).
5. Backfill with native soil or a permeable material to grade.

Holes-down placement is non-negotiable. Jobsite Calcs’ installation guide explains why: water enters the pipe from the bottom of the trench, where it collects. Holes-up forces the entire trench to saturate before any water enters the pipe, which defeats the purpose of the drain and accelerates clogging.

Pro Tip: Mark the top of the pipe with a stripe of spray paint before lowering it into the trench. That stripe stays visible during installation and confirms holes-down orientation at a glance.

Slope guidance

A laser level or a 4-foot level with a shim works well for checking this before backfilling. Flat sections trap sediment and standing water, which accelerates clogging at the low point.

Why geotextile fabric and the burrito-wrap method matter

The gravel alone won’t keep your drain open long-term. Soil particles, especially in clay-heavy Texas soils, migrate into the stone void space over time and gradually choke the system. Non-woven geotextile filter fabric stops that migration while still letting water pass freely.

Choosing the right fabric

Standard non-woven, needle-punched geotextile in the 4–8 oz/yd² range works for most residential soils. In clay-heavy conditions, go heavier (6–8 oz/yd²) to slow fine-particle migration more aggressively. Do not substitute woven landscape “weed barrier” fabric. Home Depot’s French drain guide specifically warns against weed barrier as a filter fabric substitute — it blocks water flow rather than filtering it, which turns the trench into a bathtub.

The LSU AgCenter guide recommends the burrito-wrap method as the most reliable approach for preventing soil migration and extending system life.

How to install the burrito wrap

• Drape the geotextile across the full width of the trench before any stone goes in, with enough overhang on each side to fold back over the top.
• Lay the bedding stone, set the pipe holes-down, then fill stone to within a few inches of grade.
• Fold the fabric flaps over the top of the stone, overlapping at least 6–18 inches at the center seam.
• Secure the overlap with a few shovelfuls of backfill before fully covering.

Pro Tip: In sandy or silty soils, use a heavier 6 oz/yd² fabric and check the overlap seam before backfilling. A gap at the top of the burrito wrap is the most common fabric installation error, and it creates a direct path for fines to enter the stone envelope.

Common mistakes that cause French drains to fail

Jobsite Calcs notes that a properly built French drain using clean #57 stone, a burrito wrap, holes-down pipe, and correct slope can last 20–50 years. A poorly built one clogs in 5–10 years. The gap between those outcomes comes down almost entirely to build details, not maintenance.

The most common failure modes

1. Using fines-laden aggregate (crusher run, all-purpose gravel, unwashed stone): Fines fill the void space and the drain loses permeability.
2. Skipping filter fabric or using woven weed barrier: Soil migrates into the stone within a few wet seasons.
3. Holes-up pipe orientation: The trench must fully saturate before the pipe drains, accelerating sediment buildup.
4. Insufficient slope or flat sections: Standing water and sediment accumulate at low points.
5. Too little stone above the pipe: Less than 4 inches of cover above the pipe reduces the filter zone and allows soil contact with the pipe perforations.

Pro Tip: Before backfilling, run a garden hose into the uphill end of the pipe and confirm water exits at the outlet. Then walk the trench with a 4-foot level to catch any flat sections. Both checks take under 10 minutes and can save you from digging it all up later.

How to buy and order gravel for your French drain

Understanding ordering units

Quarries sell #57 stone by the ton. Your calculation gives you cubic yards, so you’ll need to convert. Using the 1.4 tons-per-cubic-yard rule of thumb from the remodelcalculators guide, multiply your buffered cubic yard figure by 1.4 to get tons. Confirm that conversion factor with your specific supplier before placing the order.

Ordering checklist

• Calculated cubic yards (from your trench dimensions)
• 10% buffer added to the final figure
• Converted ton weight (cu yd × supplier density factor)
• Delivery gate width and height clearance noted
• Drop location marked (ideally within 50 feet of the trench)
• Offload method confirmed (dump truck tailgate, conveyor, or machine-assisted)
• HOA or permit requirements checked for material staging

Staging tips for tight yards

If your yard has limited access, request smaller loads split across two drops rather than one large delivery. A standard dump truck carries 10–14 cubic yards per load; for a small residential job under 5 cubic yards, ask about half-load options or a smaller vehicle. For material delivery in San Antonio, Olearydevelopmentgroup offers flexible drop options suited to residential sites with narrow gates or limited staging space.

Pro Tip: Confirm “washed” and “no fines” in writing when you place the order, and ask for a photo of the stockpile before delivery. If the stone arrives with visible dust or a fine coating, you have grounds to reject the load before it’s dumped.

A practical note on planning your material order

DIY French drain projects almost always encounter at least one surprise: a clay pocket that widens the trench, a root that forces a detour, or a low point that needs extra stone to maintain slope. Planning for those variables before you order is what separates a one-delivery project from a two-delivery one.

For homeowners in the San Antonio area, Olearydevelopmentgroup delivers washed and crushed gravel directly to residential sites, with GPS-tracked trucks and per-load pricing that makes it straightforward to order exactly what you need without guessing at minimums.

Olearydevelopmentgroup delivers the right gravel, on time, to your site

Getting the material spec right is half the job. Getting it delivered accurately and on time is the other half.

Olearydevelopmentgroup offers same-day and next-day bulk gravel delivery in San Antonio with per-load transparent pricing, GPS-tracked trucks, and a team that knows residential site constraints. No minimum-order guesswork, no vague density estimates. When you request a quote, specify your calculated cubic yards, confirm “washed #57 or equivalent,” note your gate width and preferred drop point, and Olearydevelopmentgroup handles the rest. Contractor accounts with net-30 invoicing are available for repeat projects.

Sources

The following references were used for calculations, specifications, and installation guidance throughout this article:

• French drain calculator
• French Drain Guide: Gravel, Pipe, Fabric & Slope
• Drainage Rock Guide: Best Gravel for French Drains | StructureSmart
• How to Install a French Drain — Step-by-Step Guide | Jobsite Calcs

FAQ

What kind of gravel do you use for French drains?

Use washed, angular #57 crushed stone (3/4-inch gradation). It maintains void space, resists compaction, and drains freely. Avoid pea gravel, crusher run, or any aggregate that contains fines.

Why does a French drain need gravel around it?

Gravel creates the permeable void space that collects groundwater and channels it toward the pipe. It also reduces hydrostatic pressure on foundations. Without sufficient stone volume, the system can’t move water fast enough during heavy rain.

How much gravel do you need for a 30-ft French drain?

For a 30-ft trench at 12 inches wide and 18 inches deep: 30 × 1.0 × 1.5 = 45 cu ft, minus pipe displacement (~2.6 cu ft), divided by 27 = roughly 1.57 cubic yards.

How deep should a French drain be?

Most residential French drains run 18–24 inches deep. That depth places the pipe below the frost line in mild climates and intercepts groundwater before it reaches a foundation or low-lying area.

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