Drain Slope Calculator
Find the total drop for a drain line, or check the slope of one you’ve run against the plumbing code minimum.
- Slope
- Percent grade
- Code minimum
- Check
- Metric
- Per 10 Ft.
Drain Runs
Items you add are saved in this browser.
| Run | Pipe | Length (Ft.) | Slope | Drop | Check | Remove |
|---|
How to Calculate Drain Pipe Slope
Drain lines run downhill so waste carries itself along. Slope is given in inches of fall per foot of run. Multiply by the length of the run to get the total drop from one end to the other.
Worked Example
Minimum Slope by Pipe Size
| Pipe Size | Minimum Slope | Percent | Drop per 10 Ft. |
|---|---|---|---|
| 2½″ or less | ¼″ per foot | 2.08% | 2½″ |
| 3″ to 6″ | ⅛″ per foot | 1.04% | 1¼″ |
| 8″ or larger | 1⁄16″ per foot | 0.52% | ⅝″ |
International Plumbing Code Table 704.1. Local codes and the Uniform Plumbing Code can differ; many inspectors expect ¼″ per foot on 3″ building drains too.
Tips
More slope is not always better: a line much steeper than code lets water run ahead of solids. Most codes also cap slope for vents and trap arms. Check fall with a level and a tape at each end, or a laser, and support the pipe so it doesn't sag between hangers.