Best Aggregate for French Drains: Complete Selection Guide

TL;DR: The best aggregate for a French drain is washed 3/4" clean stone (#57) or clean 3/4" RCA, wrapped in filter fabric around a 4" perforated pipe (holes down) sloped at 1%. Never use crusher run. The fines clog drainage and the system fails in a few years.

A French drain is only as good as the stone packed around it. Wrong stone and you'll have clogs, poor drainage, and a system that fails in a few years. Right stone and your French drain works for decades without much thought.

This guide helps you pick the right aggregate for your drainage project.

What Makes Good French Drain Aggregate?

Good drainage stone has four things going for it:

1. Proper Size

• Large enough to create void space for water flow
• Small enough to surround pipe without huge gaps
• Typically 3/4" to 1-1/2" diameter

2. Angular Shape

• Angular stones lock together
• Prevent settling and compaction
• Maintain consistent void space

3. Clean (Washed)

• No fines (dust/dirt particles)
• Fines clog drainage voids over time
• "Clean" or "washed" stone is essential

4. Durable

• Resists weathering and breakdown
• Maintains size and shape for years
• Doesn't dissolve or erode

Best Aggregate Options for French Drains

Option 1: 3/4" Clean Stone (Recommended)

Also called: 3/4" washed, #57 stone, 3/4" clear

Specs:

• Size: 3/4" to 1" diameter
• Shape: Angular (crushed) preferred
• Fines: None (washed)

Pros:

• Perfect balance of drainage and coverage
• Completely surrounds standard 4" pipe
• Easy to work with
• Widely available

Cons:

• Can shift if not contained
• Slightly more expensive than unwashed

Best for: Standard French drains, foundation drains, yard drainage

Option 2: 1" to 1-1/2" Stone

Also called: #467, 1" clean, medium drainage stone

Specs:

• Size: 1" to 1.5" diameter
• Shape: Angular
• Fines: None

Pros:

• Maximum drainage capacity
• Excellent for high-flow situations
• Less susceptible to clogging

Cons:

• Larger gaps around pipe
• May need more stone to fill trench
• Can migrate if not edged

Best for: High-volume drainage, deep French drains, commercial applications

Option 3: 3/4" Recycled Concrete (RCA)

Specs:

• Size: 3/4" to 1" (screened)
• Shape: Very angular
• Fines: Minimal to none (specify "clean")

Pros:

• Usually the most economical option
• Excellent angular shape
• Environmentally friendly
• Performs as well as virgin aggregate

Cons:

• Variable appearance
• May not be available "washed" in all areas
• Slight residue possible

Best for: Budget-conscious projects, eco-friendly installations, residential drainage

Option 4: River Rock / Pea Gravel

Specs:

• Size: Varies (typically 1/2" to 1")
• Shape: Rounded (water-worn)
• Fines: Usually none

Pros:

• Attractive appearance (for exposed applications)
• Smooth texture
• Available everywhere

Cons:

• Rounded shape = less stable
• Higher settling over time
• More expensive for comparable drainage

Best for: Decorative drains, dry creek beds, visible drainage features

What NOT to Use

Crusher Run / Dense Grade

• Contains fines that clog drainage
• Compacts into solid mass
• ZERO drainage capacity

Sand

• Too fine, fills voids
• Allows no water flow
• Will completely fail

Limestone Screenings

• Basically powder/dust
• Creates paste when wet
• Opposite of drainage

Dirty/Unwashed Gravel

• Fines clog over time
• May seem fine initially
• Fails within 3-5 years

How Much Aggregate Do You Need?

Standard French Drain Dimensions:

• Width: 6-12" (typical residential)
• Depth: 18-24" (below grade)
• Pipe: 4" perforated

Aggregate Needed (per linear foot):

• 6" wide × 18" deep: ~0.03 cubic yards
• 12" wide × 24" deep: ~0.1 cubic yards

Quick Estimate Table

Drain Length	6"×18" Trench	12"×24" Trench
25 feet	0.7 cy / 1 ton	2.5 cy / 3.5 tons
50 feet	1.4 cy / 2 tons	5 cy / 7 tons
100 feet	2.8 cy / 4 tons	10 cy / 14 tons

Formula:

(Width × Depth × Length) ÷ 324 = Cubic Yards Cubic Yards × 1.4 = Tons

Add 10% for settling and variation.

French Drain Installation with Proper Aggregate

Step 1: Dig the Trench

• Slope: 1% grade (1" drop per 8 feet)
• Width: At least 6", preferably 12"
• Depth: 18-24" for most applications
• Smooth bottom

Step 2: Line with Filter Fabric

• Drape landscape fabric along trench
• Leave excess on sides (fold over later)
• Fabric prevents soil infiltration

Step 3: Add Base Layer of Aggregate

• 2-3" of clean stone on bottom
• Level and compact lightly
• Creates bed for pipe

Step 4: Install Pipe

• Perforated pipe, holes facing DOWN
• Maintain consistent slope
• Connect sections securely
• Route to proper outlet

Step 5: Surround with Aggregate

• Fill around and over pipe
• Leave 3-4" below surface (for topsoil/sod)
• Don't compact too aggressively

Step 6: Wrap with Fabric

• Fold excess fabric over aggregate
• Overlap seams by 4-6"
• Creates complete envelope

Step 7: Cover

• 3-4" of topsoil for lawn areas
• OR leave gravel exposed for utility areas

Comparing Aggregate Costs

Material	Relative Cost	Drainage
3/4" washed stone (virgin)	Middle	Excellent
RCA #57 (clean recycled)	Usually lowest	Excellent
1" drainage stone (virgin)	Middle to higher	Excellent
River rock	Highest	Good, but rounded and less stable

Delivery is extra no matter what you buy. For current RCA #57 pricing and delivery from SMSG, call (865) 999-0857.

RCA #57 gives you the same drainage performance, usually for less.

A Few More Practical Tips

• One stone for the whole trench is fine. 3/4" clean stone works from bottom to top. Some people use larger stone on the bottom, but it's not necessary for residential drains.
• Color only matters if it shows. For buried drains, color is irrelevant. For exposed drains (like dry creek beds), choose a look you like.
• Source clean material. If your supplier doesn't offer washed stone, you can rinse it with a hose, but it's much easier to start clean.
• Reusing old gravel: if it's clean and the right size, fine. If it's full of fines or sediment, replace it.

Figuring tonnage for a long run? Our tons vs cubic yards guide walks through the math.

Signs Your Aggregate Was Wrong

If your French drain fails early, check for:

• Fines in the stone: Muddy residue in trench
• Crushed/broken aggregate: Material too soft
• Compacted solid mass: Wrong product used
• Root infiltration: Fabric failure (not aggregate fault)
• Pipe crushed: Aggregate too large, not supporting pipe

What To Use

For most French drains, 3/4" clean crushed stone or RCA is the right call. Good drainage, surrounds the pipe properly, lasts for decades.

Spend the money on clean (washed) material. Fines in cheap aggregate cause more French drain failures than any other single factor.

Related guides

• Understanding Aggregate Sizes: #57, #2, Crusher Run & More Explained: Decodes the sizing numbers so you can order #57 or #67 stone with confidence.

• Best Backfill Material for Retaining Walls: Complete Guide: Same drainage-zone logic applied to the space behind retaining walls.

• What Is Recycled Concrete Aggregate (RCA)? The Complete Guide for Contractors and Homeowners: How RCA is made and why it drains as well as virgin stone.

• Best Gravel for Standing Water in Your Yard: Diagnosing yard water before you dig.

Need drainage aggregate for your project? Smoky Mountain Sand & Gravel sells RCA #57, clean recycled concrete stone with no fines, throughout Blount County, Maryville, Alcoa, and surrounding East Tennessee communities. See our aggregate for sale page, and call us at (865) 999-0857 for current pricing and delivery.