What Size Gravel Do You Need for a French Drain?

If you’re looking to install a French drain on your property, you’ll need to know what size gravel to use. In this blog post, we’ll go over the different gravel sizes and how to choose the right one for your needs.

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A French drain is a gravel-filled trench that redirects water away from problem areas in your yard, such as wet spots in your lawn or pooling at the base of a slope. The easiest way to determine how much gravel you’ll need for your French drain is to calculate the volume of gravel needed using simple algebra.

What is a French Drain?

A French drain, also called a curtain drain, is used to collect groundwater and redirect it away from problem areas in your yard. French drains are simple systems consisting of a perforated pipe surrounded by gravel. The pipe is installed in a trench that slopes down from the area to be drained to a lower collection point, such as a storm drain or dry well.

The gravel acts as both a filter and a reservoir for water. When installed properly, French drains are highly effective at diverting water and preventing flooding and water damage. They can be used to drain wet spots in your yard, prevent basement flooding, and protect your home from water seepage.

What Size Gravel Do You Need for a French Drain?

When it comes to drainage, gravel is often used to improve existing systems or create new ones. A French drain is one of the most versatile and commonly used types of drainage systems. It can be used to direct water away from problem areas in your yard, such as near your foundation or alongside a retaining wall. French drains can also be used to create a dry riverbed in your landscape.

Gravel is an important part of a French drain because it allows water to flows freely through the system while providing adequate storage for runoff. But not all gravel is created equal. The type and size of gravel you use will vary depending on the application. Here are some general guidelines to help you choose the right gravel for your French drain:

For most residential applications, you will want to use ¼” or 3/8” gravel. This is small enough to provide adequate drainage while being large enough to prevent clogging.

If you are using a French drain in an area with heavy runoff, such as next to a downspout, you may want to use 1/2” gravel. This is also a good choice for areas with steep grades.

For very large commercial applications, such as golf courses or parks, 1” gravel may be necessary. This is also a good choice for areas that are subject to flooding or severe erosion.

Generally speaking, the larger the gravel, the less you will need (and vice versa). Use this calculator to determine how much gravel you need for your French drain:

3.1 The diameter of the pipe

A French drain is a pipe (perforated or not) placed in a bed of gravel and used to redirect groundwater away from an area. The diameter of the pipe is important as it will determine how much water the drain can handle. A 4-inch pipe is sufficient for most home applications, but you may need a larger diameter pipe if you have a lot of water flowing through your property.

The width of the trench should be at least twice the width of the pipe, and the depth should be at least 18 inches. The gravel should be placed in the trench before the pipe is installed.

3.2 The length of the trench

The length of the trench will be dependent on a few factors. The first is the size of the gravel that you have chosen. The second is the depth of the trench. You will need to excavate your trench to a depth of at least six inches. The third factor is the width of your gravel bed. You will need to have a minimum width of four inches for your French drain.

3.3 The depth of the gravel

The correct depth of gravel for a French drain is important. The general rule of thumb is that the gravel should be as deep as the footing of the house (the widest part of the concrete footer – typically 8″). However, you want to make sure that the minimum depth of gravel is at least 6″.


In conclusion, the size of gravel you need for a French drain depends on the intended purpose of the French drain, the size of the project, and the type of gravel you choose. Ultimately, you want to choose a gravel that will allow water to flow freely through it without causing too much sediment buildup.