Best Gravel for a French Drain: Type, Size and How Much You Need

Short answer: use clean, washed, angular stone about 3/4 inch in size, such as #57. HouseLogic specifically recommends clean, washed 3/4-inch stone and says to avoid fines and pea gravel, which compact (HouseLogic).

The stone in a French drain has one job: to leave open space so water can reach the pipe. Anything that packs tight or contains dust slowly chokes the drain.

This guide explains which gravel to use, how to layer the trench, and how to calculate exactly how much stone you need. For an instant number, use the French drain gravel calculator.

What type of gravel is best for a French drain?

Gravel	Good for a French drain?	Why
#57 washed stone (1”–3/16”)	✅ Best choice	Clean, angular, large voids. See #57 stone explained
#67 washed stone (3/4”–3/16”)	✅ Good	Same as #57, slightly smaller
Washed 3/4” clear stone	✅ Good	Same idea: no fines
Pea gravel	⚠️ Not ideal	Small round stones nest together and compact (HouseLogic)
Crusher run / #411 / dense grade	❌ Avoid	Stone dust fills the voids and clogs fabric and pipe
River rock (large)	⚠️ Works, costly	Drains, but more expensive and harder to place

Key rule: the gravel must be washed. The word “clean” on a quarry ticket means the dust has been removed.

What size gravel for a French drain?

Aim for about 3/4 inch (HouseLogic), which is exactly the range covered by ASTM sizes #57 (1 inch to No. 4) and #67 (3/4 inch to No. 4) (ASTM D448).

Stone this size is large enough to leave open channels for water. It is still small enough to bed the pipe firmly and shovel easily.

How a French drain is layered

Typical construction, from the bottom up, per HouseLogic and HGTV:

1. Trench: HouseLogic suggests 12–18 inches wide and 18–24 inches deep, sloped at about 1%, roughly 1 inch of drop every 8–10 feet. HGTV gives a similar fall of about 6 inches over 50 feet (HGTV).
2. Filter fabric: line the trench with non-woven filter fabric, leaving enough overhang to wrap over the top. This keeps soil from silting the drain shut.
3. Bedding stone: 2–3 inches of washed gravel under the pipe.
4. Perforated pipe: laid with the holes facing down (HouseLogic).
5. Gravel cover: fill with washed gravel to a few inches below grade.
6. Wrap and finish: fold the fabric over the stone, then top with soil, sod or decorative stone.

How much gravel do I need for a French drain?

Calculate the volume of the trench, then subtract the space the pipe takes up. For 4-inch pipe the pipe volume is small, so most people simply calculate the full trench.

Cubic yards = length (ft) × width (ft) × gravel depth (ft) ÷ 27

Example: a 50-ft trench, 12 inches wide, with 18 inches of gravel

1. 50 × 1 × 1.5 = 75 cubic feet
2. 75 ÷ 27 = 2.78 cubic yards
3. 2.78 × 1.4 ≈ 3.9 tons. Dry gravel is about 105 lb/ft³ (Engineering ToolBox).
4. Volume of the 4-inch pipe: π × (2/12)² × 50 ≈ 4.4 cubic feet, about 0.16 yd³. It can safely be ignored.

Gravel per 10 feet of trench

Trench width × gravel depth	Cubic feet per 10 ft	Cubic yards per 10 ft
6 in × 12 in	5.0	0.19
12 in × 18 in	15.0	0.56
12 in × 24 in	20.0	0.74
18 in × 24 in	30.0	1.11

Multiply by your trench length ÷ 10, and add 5–10% for waste. The French drain gravel calculator handles any trench size.

Common French drain gravel mistakes

• Using crusher run or unwashed stone. The dust clogs the fabric and pipe.
• Using pea gravel. It compacts and reduces flow (HouseLogic).
• Skipping filter fabric. Soil migrates into the stone over time.
• No slope. Without about 1% fall, water sits in the pipe instead of flowing out.
• Too little stone over the pipe. Cover the pipe fully before folding the fabric over.

How much does French drain gravel cost?

Washed drainage stone typically costs about $25–$50 per ton or $30–$70 per cubic yard, delivered. That is HomeGuide’s range for “aggregate & drainage rock” (HomeGuide).

For the 50-ft example above (about 3.9 tons), expect roughly $100–$200 in stone before delivery. See the gravel cost guide for delivery fees.

Frequently asked questions

What is the best gravel for a French drain? Clean, washed, angular stone about 3/4 inch, such as #57 or #67.

Can I use pea gravel for a French drain? It isn’t recommended. Small, round stones nest together and compact, which reduces flow.

How deep should gravel be in a French drain? Common guidance is a trench 18–24 inches deep, filled with gravel to a few inches below grade, with 2–3 inches of stone under the pipe.

Do you need fabric in a French drain? Yes. Non-woven filter fabric keeps soil out of the stone and pipe.

Sources

• HouseLogic, How to Install a French Drain, Step by Step: houselogic.com
• HGTV, How to Install French Drains: hgtv.com
• ASTM D448, Standard Classification for Sizes of Aggregate, Table 1: PDF copy
• HomeGuide, How Much Does Crushed Stone or Gravel Cost? (2026): homeguide.com
• Engineering ToolBox, Dirt and Mud – Densities: engineeringtoolbox.com