Drain Slope Calculator
Calculate the correct slope (grade) for drain pipes based on pipe diameter and run length. This calculator uses IPC/UPC plumbing code minimum slopes to verify your drainage installation will flow properly and pass inspection.
Enter Pipe Details
Full Breakdown
Pipe Diameter
Pipe Run
Slope (in/ft)
Slope (%)
Total Drop
Code Minimum
Compliance
How to Use This Calculator
- Select the pipe diameter for your drain line.
- Enter the pipe run length in feet (horizontal distance).
- Optionally enter a custom slope or leave blank to use the code minimum.
- Click "Calculate Slope" to see the required drop and compliance status.
- Use "Find Slope" mode to check if an existing installation meets code.
The Formula
Total Drop (inches) = Slope (in/ft) × Pipe Length (ft)
Grade (%) = (Slope in/ft ÷ 12) × 100
IPC/UPC Code Minimum Slopes
- Pipes 2½" and smaller: ¼ inch per foot (0.25 in/ft = 2.08%)
- Pipes 3" to 6": ⅛ inch per foot (0.125 in/ft = 1.04%)
- Pipes 8" and larger: 1/16 inch per foot (0.0625 in/ft = 0.52%)