French Drain Calculator
Free french drain calculator. Enter trench length, width and depth to get the gravel you need in cubic yards and tons, plus drain pipe length and fabric.
About This Free Online French Drain Calculator
Our free french drain calculator sizes the materials for a gravel-filled trench drain. Enter the trench length, width and depth and the perforated pipe diameter, and the tool returns the gravel you need in cubic yards and tons (after subtracting the pipe volume), the drain pipe length, and the landscape fabric area to line the trench. Use washed #57 stone and a 4 inch corrugated pipe for a typical residential drain. Every calculation runs in your browser with no signup — ideal for landscapers, homeowners and drainage contractors on site.
Features of Our French Drain Calculator
- Gravel in cubic yards and tons (pipe volume subtracted)
- Drain pipe length to match the trench
- Landscape fabric area for bottom and both walls
- Adjustable trench width, depth and pipe diameter
- Works for curtain drains, footer drains and swales
- 100% client-side and private — no signup, no data sent
How to Use the French Drain Calculator
Using this tool is simple and requires no signup or registration. Follow these steps:
- Enter the trench length in feet, and the width and depth in inches.
- Set the perforated pipe diameter (4 inch is typical).
- Read the gravel order in cubic yards and tons.
- Note the drain pipe length and fabric area to buy.
Frequently Asked Questions About French Drain Calculator
How much gravel do I need for a french drain?
Multiply trench length × width × depth to get cubic feet, convert to cubic yards by dividing by 27, then subtract the volume the perforated pipe takes up. This calculator does all of that and also estimates tons at 1.4 tons per yard.
What size gravel is best for a french drain?
Washed #57 stone (roughly 1/2 to 1 inch) is the standard — it drains freely and locks together around the pipe. Avoid pea gravel and sand, which clog. Enter your trench size and the calculator sizes the order.
Why subtract the pipe volume?
The perforated pipe occupies space inside the trench, so that volume is not filled with gravel. Subtracting it (which this calculator does automatically) prevents over-ordering stone.
How deep should a french drain be?
Most residential french drains are 18 to 24 inches deep and wide enough for a 4 inch pipe plus gravel on both sides. Deeper drains carry more water and protect foundations below the frost line.
Is this french drain calculator free?
Yes, completely free with no signup. Every estimate runs in your browser, so nothing is uploaded or tracked.
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