Drain slope calculator
Estimate outputs: Total fall, Ending invert level. Adjust Pipe run, Required slope, Starting invert level to match your project.
Estimate outputs: Total fall, Ending invert level. Adjust Pipe run, Required slope, Starting invert level to match your project.
Inputs and units
Use the units shown beside each field. Replace the sample values with your measurements and the figures on the selected product packaging.
| Parameter | Example input |
|---|---|
| Pipe run | 20 m |
| Required slope | 1 % |
| Starting invert level | 100 m |
Formula and assumptions
Total fallPipe run × Required slope / 100
Ending invert levelStarting invert level - Total fall
ceil = round up; floor = round down; max = the greater value. Trigonometric angles are converted from degrees to radians.
Allowance is applied before rounding to whole packages. Whole units are rounded up; displayed decimals are rounded only for readability.
This is a preliminary geometry or quantity calculation, not a design check. Dimensions, spacing and performance requirements must come from your project.
Worked example
Sample values are examples, not product specifications. Run the calculation again with your own measurements.
| Result | Calculation |
|---|---|
| Total fall | 0.2 m |
| Ending invert level | 99.8 m |
Related calculators
Related tools use separate measurements. Check their inputs before transferring quantities.
These are quantity estimates. Confirm product coverage, site conditions and required dimensions before ordering.