Free-Draining Rock for French Drains, Trenches & Drainage Systems — Delivered Across Marin, Sonoma, Alameda, Contra Costa, San Francisco & San Mateo
 
Drain Rock Gravel is a clean, angular-to-rounded rock designed to move water fast and keep drainage systems working long-term. It’s one of the most requested materials for French drains, trench drains, footing drains, retaining wall backfill, and yard drainage projects across the North Bay and Bay Area—especially in areas with seasonal rain and heavy clay soils.
 
At North Bay Materials, we deliver drain rock by the ton in multiple sizes so you can match the rock to your specific application:
Available sizes: 1/4", 5/16", 3/8", 1/2", 3/4", 1 1/2", 3", 6"
Whether you’re building a backyard French drain in San Rafael, replacing wet soil behind a retaining wall in Mill Valley, or trenching for utilities in Walnut Creek, drain rock helps prevent pooling, reduces hydrostatic pressure, and improves water flow where it matters most.
 
Choosing the Right Drain Rock Size
Match Rock Size to Drainage Performance & Application
Selecting the correct drain rock size is critical for water flow, stability, and long-term performance. North Bay Materials offers a full range of drain rock sizes by the ton so contractors and homeowners can dial in the right solution for each project across Marin, Sonoma, Alameda, Contra Costa, San Francisco, and San Mateo counties.
 
Drain Rock Size Guide & Common Uses:
1/4" – 5/16"
Best for light drainage, planter boxes, permeable paver base and shallow landscape drains where smaller void spaces are needed. Often used around small perforated pipes with filter fabric.
 
3/8" – 1/2"
Ideal for French drains, trench drains, and utility backfill. These sizes balance water flow and compaction resistance, making them a popular all-around drainage rock.
 
3/4" (Most Common Drain Rock)
The industry standard for French drains, retaining wall backfill, and footing drains. Excellent water permeability with minimal clogging when installed with fabric.
 
1 1/2"
Used for high-volume drainage, deep trenches, and areas with heavy water flow. Provides large voids for fast water movement.
 
3" – 6"
Designed for large drainage channels, culverts, erosion control, and slope protection. Common on rural properties, vineyards, and commercial sites where structural drainage is required.
 
Pro tip:
For most residential drainage projects in the North Bay, 3/4" drain rock wrapped in filter fabric delivers the best balance of flow, durability, and cost.
 
Common Drainage Applications & Where Drain Rock Performs Best
Proven Solutions for Water Management Across the North Bay & Bay Area
Drain Rock Gravel is engineered for water movement, pressure relief, and long-term durability. It’s a foundational material for both residential and commercial drainage systems—especially in regions with clay soils, sloped terrain, and winter rainfall like Marin, Sonoma, Alameda, Contra Costa, San Francisco, and San Mateo counties.
 
Typical applications include:
French drains & perimeter drains
Creates open voids around perforated pipe, allowing groundwater to flow freely away from structures, yards, and hardscapes.
 
Retaining wall backfill
Reduces hydrostatic pressure behind walls, preventing bulging, cracking, and premature failure—critical for hillside properties in areas like Mill Valley, Tiburon, and Orinda.
 
Footing & foundation drainage
Installed around building footings to redirect water and protect slabs, basements, and crawl spaces from moisture intrusion.
 
Trench drains & utility lines
Ideal for backfilling trenches around plumbing, electrical, and irrigation lines where drainage and stability are required.
 
Yard drainage & soggy areas
Helps correct standing water issues in lawns, side yards, and low spots common in flat or poorly draining soils.
 
Erosion control & high-flow areas
Larger sizes (3"–6") are used in swales, ditches, culverts, and slope protection to slow water velocity and prevent washouts.
Because drain rock contains little to no fines, it resists clogging and maintains drainage performance over time—especially when paired with non-woven filter fabric.
 
Coverage Rates, Weight & How Much Drain Rock to Order
Estimate Quantity by the Ton for Reliable Drainage Performance
Drain Rock Gravel is sold by the ton, making it easier to calculate quantities for trenches, French drains, and structural drainage projects. Because drain rock contains minimal fines, it does not compact significantly, so accurate ordering upfront is important.
 
Typical coverage per ton (approximate):
1 ton ≈ 0.70–0.75 cubic yards
1 ton covers ~90–110 sq ft at 2" depth
1 ton covers ~45–55 sq ft at 4" depth
1 ton covers ~30–35 sq ft at 6" depth
Common drainage trench estimate:
12" wide × 18" deep trench ≈ 1 ton per 6–7 linear feet
 
Recommended ordering tips:
Add 5–10% extra for waste, uneven trenching, and grade adjustments
For long French drains or retaining walls, ordering slightly more avoids cold joints and thin sections
Larger rock sizes (1½" and up) may cover slightly more area due to increased void space
Use quote request form for large bulk orders
 
Contractors and homeowners across San Rafael, Novato, Petaluma, Walnut Creek, Concord, San Francisco, and San Mateo rely on these estimates to size projects accurately and keep installations moving without delays.
 
 
Frequently Asked Questions
Q: Which size drain rock should I use for my project?
A:
5/16" or 3/8": For planter beds, paver base, small trench drains, utility backfill, and general landscaping.
1/2" or 3/4": For most French drains, driveway base, and retaining wall backfill, and landscaping.
1-1/2": For heavy drainage fields and slope stabilization.
3" & 6": For rip rap erosion control, culvert outlets, construction entrances and shoreline reinforcement.