Ideal French Drain Gravel Size For Your Yard: Everything You Need To Know

You generally want to ensure that no one can see the trench while installing a french drain. Additionally, it would help if you chose a specific french drain gravel size. 

There are several things you need to know about gravel before you begin. How much space must you cover? What kind of gravel ought to be applied? Based on local conditions, is that particular gravel that performs better than others? This article will assist you in picking and utilizing gravel for your french drain.

What Is Gravel?

Gravel is a sedimentary rock formed from the breakdown of other rocks. It’s a loose material that you can use to grade slopes, stabilize roadways, and build drainage channels. There are many types of gravel, each with its characteristics.


The best gravel for a french drain will depend on where you live, the type of soil in your landscape, and other factors. 

You can also use different types of gravel for other parts of the same french drain, which comes in many french drain gravel sizes; understanding these french drain gravel sizes can help you select the best gravel for your situation.

Basics Of French Drains

A french drain takes water from a particular area, such as the ground near a home foundation, to stop it from harming the structure. To do this, you need a sloped ditch or trench with the high point located at the region you have to drain; the slope should be between one and two percent from end to end.


The trench’s bottom covers with a layer of gravel, and several inches of coarse sand is placed on top of that. Some french drains cover the sand beneath them with sod to conceal them and maintain their structural durability. Others have a drain pipe in the bottom.

Simple Gravel Base

In the absence of a perforated pipe, fill the bottom layer of the trench with gravel until it is two-thirds full, forming an underground river through which the water can flow. The french drain gravel size of the gravel used for this layer, which ranges from 1/2 inch to 1 inch, determines how well water flows through it and how often clogs and jams occur. 

Choose larger gravel, like 1 1/2 inches wide, for a French drain without a perforated pipe. Pea gravel, which is smaller gravel, would need more water movement.

Choose washed gravel or stone over any other type because small dust and particles can obstruct or even stop the water flow.

Hard Rock Rules

Since hard rocks like granite and river gravel won’t deteriorate as quickly as other rock types like sandstone and limestone over time, they make good choices for a french drain.

As it obtains from dried river beds before being cleaned and sold to the public, river gravel has already eroded considerably to its current french drain gravel size.

Top Layers

Whether or not a perforated pipe uses in the drain, coarse sand serves as the filler for the top few inches of a french drain. Coarse sand has been cleaned to remove contaminants and doesn’t clump or clog.

If you prefer the look of stone and don’t want to conceal the drain, you can add decorative large pebbles or sod on top of the sand after laying a weed barrier fabric over the sand layer. Rock on top also makes it possible to locate the drain the following week or years from now to assess how well it is functioning.

Why Is French Drain Gravel Size Important?

The french drain gravel size you use is the most important measurement when determining the success of your installation. With the right french drain gravel size, you can ensure your gravel settles appropriately and has the correct depth for proper drainage. 

When installing a french drain, it’s important to use coarse gravel no smaller than 3/4”. This will allow the water to flow freely through the gravel while preventing clogs.

You can use a french drain to divert surface water from your home into a storm drain. The key to successful drainage is ensuring the right french drain gravel size.

How To Select The Right French Drain Gravel Size?

The french drain gravel size is essential since it will use to collect and redirect water. Smaller gravel pieces are better for places where there is less water. Larger gravel pieces will work well for areas with a lot of water flow. 

Remember that gravel should make up about 60% of the base of your french drain; the rest is made of sand and dirt.

The French Drain Excavation Calculator can help determine how much gravel you need to buy. It can also help you determine the french drain gravel size you need. Once you have that information, you can start looking for gravel.

Types Of Gravel For French Drains

There are multiple types of gravel you can use for a french drain, but all of them work the same way:

  • Crushed Stone – Crushed stone is typically made from granite or limestone. It’s a common choice for french drains because it’s easy to find and relatively inexpensive.

Crushed stone is heavy and expensive to transport, so there may be better options if you are trying to save money.

  •  Stone Dust – Stone dust is made from crushed pieces of stone, but it tends to be less expensive than crushed stone. It’s also lighter and easier to transport. 
  •  Pea Gravel – Pea gravel, or decorative gravel, is a small pebble often used on driveways and walkways.

You’ll find little gravel, so it’s typically not a good choice for French drains. It tends to clog up the gravel and prevent water from flowing through the trench.

  • Rocks – While rocks won’t be effective for a french drain, they can be helpful for other gardening projects. Rocks can be a cheap way to fill your french drain. They may not be as effective as different types of gravel, but they work just as well.

The type of gravel you choose depends on your needs and what you have available in your surrounding area.

How To Measure Your Area For Gravel?

As you plan your french drain, measure the area where the water will run. You want to know how many cubic feet of gravel you need to cover the area. The amount of gravel you need will vary based on the gravel’s size and the trench’s size. 

If you calculate how much gravel you need to cover a specific area, you don’t know how much soil you’ll need to protect it. You want the gravel to sit at least two to three inches below the surface. 

You also want enough soil to cover the gravel and extend out past the ends of the trench.

How To Install A French Drain With Gravel?

Installing a french drain with gravel is a two-part process. First, excavate the trench, then place the gravel in the bottom of the trench. 

After excavating the trench, use a level to ensure the sides are straight. Then, use a shovel to place the gravel in the bottom of the trench. 


Make sure to fill it up to the top. After the gravel is in place, use a shovel or trowel to fill the trench with sand and soil carefully. Be careful to keep the gravel intact as you work.

Why Should You Avoid Small Gravel When Installing A French Drain?

French drains often use small gravel to create a layer that allows water to flow freely through the system. As discussed above, the smaller gravel used in the french drain can prevent large particles such as rocks, tree branches, and other debris from entering the drain. 

However, if the gravel is too small, it can get clogged with organic matter such as leaves or twigs. This can block the drain and prevent water from flowing freely.

A french drain clogged with leaves or other organic matter will fail to protect your home from excessive moisture. The excess water might end up causing mold and further damage your walls, floors, and other parts of the house.

Final Thought

One of the benefits of using gravel for a french drain is that it is relatively cheap. You can save money and time by selecting the right french drain gravel size. Choosing gravel that is easier to install will also save you time.

Make sure you choose coarse gravel no smaller than 3/4” in diameter. This will ensure that the water can flow freely through the gravel without becoming clogged.  

If you are still determining whether you have the necessary equipment or know-how to install a french drain, you should consider hiring a contractor. 

However, you can complete most of the work if you have the required knowledge. You can make a french drain that looks good and works even better with the help of gravel.

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Michael Bowen

Michael Bowen

Michael Bowen is an ambitious entrepreneur who has been in the business of building homes since he was 19. Michael's commitment to honesty, integrity, and high-quality workmanship has earned him a reputation as one of the best in the business.

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