1. What is French Drain Pipe Size?

The French drain pipe size determines the appropriate diameter of perforated pipe needed to handle a specific water flow rate at a given velocity. Proper sizing ensures efficient drainage and prevents system overload.

2. How Does the Calculator Work?

The calculator uses the basic pipe sizing formula:

Where:

• \( Flow\ Rate \) — Water flow rate in gallons per minute (GPM)
• \( Velocity \) — Water velocity in feet per second (ft/s)

Explanation: The formula calculates the minimum pipe diameter needed to handle the specified flow rate at the desired velocity.

3. Importance of Proper Pipe Sizing

Details: Correct pipe sizing prevents water backup, ensures efficient drainage, and maintains proper system function over time.

4. Using the Calculator

Tips: Enter flow rate in GPM and desired velocity in ft/s. Typical velocity ranges from 2-5 ft/s for drainage applications.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical flow rate for residential French drains?
A: Most residential systems handle 5-20 GPM, depending on roof size and rainfall intensity.

Q2: Why is velocity important in pipe sizing?
A: Proper velocity ensures self-cleaning (prevents sediment buildup) while avoiding erosion from excessive speed.

Q3: What pipe material is best for French drains?
A: Corrugated perforated PVC or HDPE pipes are most common, with sizes typically 4-6 inches for residential use.

Q4: Should I round up the calculated size?
A: Yes, always round up to the next available standard pipe size for safety margin.

Q5: How does slope affect pipe sizing?
A: Steeper slopes increase velocity, which may allow smaller pipes, but minimum sizes are often dictated by practical installation considerations.