Drainage Slope Calculator
Calculate required vertical drop for drainage lines from horizontal run and target slope.
30 ft run at 0.125 in/ft =
3.75 in drop
Representative value from the Drainage Slope Calculator reference table.
Reference Values
Browse 40 reference values with individual detail pages for quick lookup.
Drainage Slope Calculator
Compute vertical drop from run length and planned drainage slope.
Calculated Drop
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Reference Table
Use this complete table for quick lookup and internal linking to specific value pages.
| 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
Common questions about Drainage Slope Calculator, formulas, and typical use cases.
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
This page combines a live calculator, precomputed reference values, and FAQ content from the same conversion definition to reduce mismatch between calculator output and lookup tables.
Editorial metadata (author, reviewer, and update date) is rendered on the page and in structured data. See our editorial policy, review process, and corrections policy.
For compliance-sensitive work, verify final values against project requirements, governing standards, and manufacturer documentation.