French Drain Gravel, Pipe and Fabric Calculator
Estimate drainage gravel, perforated pipe length and filter fabric for a rectangular French drain trench.
Formula
Planning estimate. Check product specifications and local requirements before purchasing.
Worked example: French Drain Calculator
Measurements in this example
| Trench length | 20 m |
|---|---|
| Trench width | 0.4 m |
| Trench depth | 0.6 m |
| Pipe diameter | 110 mm |
| Waste allowance | 10 % |
Calculated quantities
| Drainage gravel | 5.07 m³ |
|---|---|
| Total length | 21 m |
| Filter fabric | 35.2 m² |
What to check
This calculation uses: Trench length, Trench width, Trench depth, Pipe diameter, Waste allowance. It returns: Drainage gravel, Total length, Filter fabric.
Take dimensions at several points because trenches and excavations rarely have perfectly square sides or a level base.
Use the result to plan supply and transport, then check ground conditions, compaction and disposal rules with the contractor.
Services, unstable sides, groundwater and safe working slopes are not quantities that a volume calculation can resolve.
Use the units beside each field. The values in the worked example are starting inputs; replace them with your measurements and the specifications of your material.
Compare alternatives
Open a tool, enter your measured dimensions, then save an estimate. Keep another version if you want to compare products or allowances.