Drain Pipe Slope
Slope (in per ft) × run length = total drop. Standard ¼" per ft.
Result
Total drop
7.50"
30 ft × 0.25"/ft. Recommended for 3": ⅛"/ft.
- Pipe diameter3"
- Run30 ft
- Slope0.25"/ft
- Slope %2.08%
- Total drop7.50"
- Recommended⅛"/ft
Step-by-step
- Drop = run × slope = 30 × 0.25 = 7.50 inches.
- Slope as % = 0.25/12 × 100 = 2.08%.
How to use this calculator
- Enter pipe size + run length.
- Pick slope (¼"/ft standard).
- Read drop.
About this calculator
Drain pipes need slope so water carries solids. IPC standard: ¼" per foot (2.08% slope) for pipes ≤ 2.5". For 3" and larger, ⅛" per ft (1.04%) is acceptable and often required (steeper = water races ahead, leaves solids behind). Too flat: water doesn't flow, sediment builds up. Too steep: liquid outpaces solids → blockage. Building codes typically require ¼" per ft for residential drain lines.
Frequently asked
Big pipes carry water in shallow stream — needs only gentle slope. Steep slope outruns solids.
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