French drains are an effective way to save money on irrigation and drainage. In order to be effective, they must be properly designed and constructed. In order to save the most money with a french drain, you will need to calculate your costs in advance using a french drain cost calculator . The best way to do this is to use our free french drain cost and gravel calculators.

Designing a french drain system takes a little math and a lot of knowledge about your yard. In order to design a tench drain system, you will need to know the following information:

- How much water does your drainage area remove?
- What is the slope of the ground around it?
- What is the average rainfall in your area?
- How much perforated pipe is needed?

Use our french drain calculator to determine the exact piping, gravel and estimate the total cost of french drain installation on your property.

**French Drain Cost Calculator**

Once you have this information, use our french drain cost calculator to determine how much it will cost for you to install your french drain. Most people save more than $100 per year on their irrigation costs by installing a french drain in their yard. This equals about $8 per month or even more in savings, depending on the size of your property.

**French Drain Gravel Calculator**

One of the most important components of your french drain will be the gravel. Use our free french drain gravel calculator to determine how many bags of gravel you need to line your trench. Each bag of gravel costs about $12.00, so you will save money by calculating the exact amount your need in advance!

**Frequently Asked Questions**

Learn more about calculating the exact amount of gravel and total cost of your backyard french drain.

**How do you calculate the size of a French drain?**

**T**o calculate the size of a french drain, multiply all surface area, slope and average rainfall.

**How much gravel do I need for a 100 foot French drain?**

To calculate gravel needed for a 100′ french drain, multiply the length of the trench by the width and depth. If you plan to lay down 4 inches of gravel, multiply 100 feet x 4 inches = 400 cubic feet. Since each bag equals 1.5 cubic feet, divide 400 by 16 to determine the number of bags you will need about 26 bags.

**How much gravel do I need for a 50 foot French drain?**

To calculate gravel needed for a 50′ french drain, multiply the length of the trench by the width and depth. If you plan to lay down 4 inches of gravel, multiply 50 feet x 4 inches = 200 cubic feet. Since each bag equals 1.5 cubic feet, divide 200 by 16 to determine the number of bags you will need about 13 bags of gravel.

**How much is a French drain per foot?**

The average french drain costs between $450 and $550, or about $3-4/per linear foot for materials and labor. The more surface area you cover in the trench, the higher the cost.