About this calculator
Total drop for a drain or waste pipe at a given gradient, so you can set invert levels at each end.
How it’s calculated
Fall = length ÷ gradient ratio. ¼" per foot = 1:48 ≈ 2%.
Worked example
With these inputs:
- Pipe run length
- 40 ft
- Gradient
- ¼" per foot (2%)
the result is:
- Total fall
- 10"
- Gradient
- 1:48 = 2.08%
- Angle
- 1.19°
- Fall per foot
- 1/4"
Tips from the trade
- Most codes require ¼" per foot for pipes 2½" and smaller, and ⅛" per foot for 3"+ in many cases.
- Too steep can be as bad as too flat: water outruns the solids.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and local building codes before ordering.