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French Drain Calculator
Size the trench and this returns the stone, pipe and fabric, plus the fall you need across the run for it to actually drain.
Your numbers
Result
Drainage stone
3.14
cubic yards
- Stone in tons
- 4.24tons
- Perforated pipe5% over for cuts
- 63linear ft
- Filter fabric
- 300sq ft
- Total fall neededAcross the whole run
- 7.2in
- Trench volume
- 90cubic feet
- Spoil to remove
- 4.17cubic yards
How this is calculated
- Trench volume = length × (width ÷ 12) × (depth ÷ 12).
- Gravel = trench volume − the volume the pipe displaces.
- Fabric = length × (trench width + both trench walls + overlap).
- Fall = length × slope %. At 1%, a 60 ft run needs about 7 inches of drop.
Before you order
- Wrap the stone in filter fabric, not the pipe. Sock-wrapped pipe sitting in soil clogs; fabric around the whole stone envelope keeps fines out and is what makes the drain last.
- Perforations face DOWN. Water enters the pipe from below through the stone once it rises — this is the single most common installation error.
- Use clean, washed, angular stone. Rounded pea gravel and anything with fines in it will silt up.
- The drain has to go somewhere — daylight, a dry well or a storm connection. A French drain that ends in the middle of a yard just moves the puddle.
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