Drainage Slope Calculator Reference Values
Calculate required vertical drop for drainage lines from horizontal run and target slope.
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Reference Value Index
This page lists 40 reference values for quick browsing and lookup.
All Reference Values
- 5 ft run at 0.125 in/ft = 0.625 in drop
- 5 ft run at 0.25 in/ft = 1.25 in drop
- 5 ft run at 0.5 in/ft = 2.5 in drop
- 5 ft run at 1 in/ft = 5 in drop
- 10 ft run at 0.125 in/ft = 1.25 in drop
- 10 ft run at 0.25 in/ft = 2.5 in drop
- 10 ft run at 0.5 in/ft = 5 in drop
- 10 ft run at 1 in/ft = 10 in drop
- 15 ft run at 0.125 in/ft = 1.875 in drop
- 15 ft run at 0.25 in/ft = 3.75 in drop
- 15 ft run at 0.5 in/ft = 7.5 in drop
- 15 ft run at 1 in/ft = 15 in drop
- 20 ft run at 0.125 in/ft = 2.5 in drop
- 20 ft run at 0.25 in/ft = 5 in drop
- 20 ft run at 0.5 in/ft = 10 in drop
- 20 ft run at 1 in/ft = 20 in drop
- 25 ft run at 0.125 in/ft = 3.125 in drop
- 25 ft run at 0.25 in/ft = 6.25 in drop
- 25 ft run at 0.5 in/ft = 12.5 in drop
- 25 ft run at 1 in/ft = 25 in drop
- 30 ft run at 0.125 in/ft = 3.75 in drop
- 30 ft run at 0.25 in/ft = 7.5 in drop
- 30 ft run at 0.5 in/ft = 15 in drop
- 30 ft run at 1 in/ft = 30 in drop
- 40 ft run at 0.125 in/ft = 5 in drop
- 40 ft run at 0.25 in/ft = 10 in drop
- 40 ft run at 0.5 in/ft = 20 in drop
- 40 ft run at 1 in/ft = 40 in drop
- 50 ft run at 0.125 in/ft = 6.25 in drop
- 50 ft run at 0.25 in/ft = 12.5 in drop
- 50 ft run at 0.5 in/ft = 25 in drop
- 50 ft run at 1 in/ft = 50 in drop
- 75 ft run at 0.125 in/ft = 9.375 in drop
- 75 ft run at 0.25 in/ft = 18.75 in drop
- 75 ft run at 0.5 in/ft = 37.5 in drop
- 75 ft run at 1 in/ft = 75 in drop
- 100 ft run at 0.125 in/ft = 12.5 in drop
- 100 ft run at 0.25 in/ft = 25 in drop
- 100 ft run at 0.5 in/ft = 50 in drop
- 100 ft run at 1 in/ft = 100 in drop
Reference Table
| Drain Scenario | Drop (in) | Drop (ft) | Slope (%) |
|---|---|---|---|
| 5 ft run at 0.125 in/ft | 0.625 in drop | 0.052 | 1.042 |
| 5 ft run at 0.25 in/ft | 1.25 in drop | 0.104 | 2.083 |
| 5 ft run at 0.5 in/ft | 2.5 in drop | 0.208 | 4.167 |
| 5 ft run at 1 in/ft | 5 in drop | 0.417 | 8.333 |
| 10 ft run at 0.125 in/ft | 1.25 in drop | 0.104 | 1.042 |
| 10 ft run at 0.25 in/ft | 2.5 in drop | 0.208 | 2.083 |
| 10 ft run at 0.5 in/ft | 5 in drop | 0.417 | 4.167 |
| 10 ft run at 1 in/ft | 10 in drop | 0.833 | 8.333 |
| 15 ft run at 0.125 in/ft | 1.875 in drop | 0.156 | 1.042 |
| 15 ft run at 0.25 in/ft | 3.75 in drop | 0.313 | 2.083 |
| 15 ft run at 0.5 in/ft | 7.5 in drop | 0.625 | 4.167 |
| 15 ft run at 1 in/ft | 15 in drop | 1.25 | 8.333 |
| 20 ft run at 0.125 in/ft | 2.5 in drop | 0.208 | 1.042 |
| 20 ft run at 0.25 in/ft | 5 in drop | 0.417 | 2.083 |
| 20 ft run at 0.5 in/ft | 10 in drop | 0.833 | 4.167 |
| 20 ft run at 1 in/ft | 20 in drop | 1.667 | 8.333 |
| 25 ft run at 0.125 in/ft | 3.125 in drop | 0.26 | 1.042 |
| 25 ft run at 0.25 in/ft | 6.25 in drop | 0.521 | 2.083 |
| 25 ft run at 0.5 in/ft | 12.5 in drop | 1.042 | 4.167 |
| 25 ft run at 1 in/ft | 25 in drop | 2.083 | 8.333 |
| 30 ft run at 0.125 in/ft | 3.75 in drop | 0.313 | 1.042 |
| 30 ft run at 0.25 in/ft | 7.5 in drop | 0.625 | 2.083 |
| 30 ft run at 0.5 in/ft | 15 in drop | 1.25 | 4.167 |
| 30 ft run at 1 in/ft | 30 in drop | 2.5 | 8.333 |
| 40 ft run at 0.125 in/ft | 5 in drop | 0.417 | 1.042 |
| 40 ft run at 0.25 in/ft | 10 in drop | 0.833 | 2.083 |
| 40 ft run at 0.5 in/ft | 20 in drop | 1.667 | 4.167 |
| 40 ft run at 1 in/ft | 40 in drop | 3.333 | 8.333 |
| 50 ft run at 0.125 in/ft | 6.25 in drop | 0.521 | 1.042 |
| 50 ft run at 0.25 in/ft | 12.5 in drop | 1.042 | 2.083 |
| 50 ft run at 0.5 in/ft | 25 in drop | 2.083 | 4.167 |
| 50 ft run at 1 in/ft | 50 in drop | 4.167 | 8.333 |
| 75 ft run at 0.125 in/ft | 9.375 in drop | 0.781 | 1.042 |
| 75 ft run at 0.25 in/ft | 18.75 in drop | 1.563 | 2.083 |
| 75 ft run at 0.5 in/ft | 37.5 in drop | 3.125 | 4.167 |
| 75 ft run at 1 in/ft | 75 in drop | 6.25 | 8.333 |
| 100 ft run at 0.125 in/ft | 12.5 in drop | 1.042 | 1.042 |
| 100 ft run at 0.25 in/ft | 25 in drop | 2.083 | 2.083 |
| 100 ft run at 0.5 in/ft | 50 in drop | 4.167 | 4.167 |
| 100 ft run at 1 in/ft | 100 in drop | 8.333 | 8.333 |
Frequently Asked Questions
Frequently asked questions for Drainage Slope Calculator and its reference values.
How is drainage drop calculated?
Drop equals horizontal run multiplied by slope in inches per foot.
What does a slope of 1/4 in per foot mean?
It means the pipe drops 0.25 inches vertically for every 12 inches of horizontal run.
Why convert slope to percent grade?
Percent grade is commonly used for site and civil coordination, while in/ft is common in plumbing layout.
Is steeper slope always better?
Not always. Excessive slope can separate liquids and solids in gravity drainage systems, so follow code and design guidance.
Methodology and Review
Each row on this page links to a value detail page derived from the same conversion data file as the main calculator and reference table. This reduces inconsistencies across page variants.
Editorial metadata and structured data are rendered across the converter page and linked value pages. Review policies are documented in our review process and editorial policy.