Calculators
Drain Slope Calculator
Calculate the total drop and percentage grade for a drain pipe from its length and slope, and check common minimum slopes.
- Runs in your browser
- Nothing uploaded
The tool
Enter your numbers below. Results update as you type, and nothing leaves your browser.
Everything you enter stays on your own machine. Nothing is sent to us or to anyone else, which you can confirm in your browser network tab.
What people use it for
- Laying out drain and sewer lines
- Checking basement bathroom feasibility
- Setting trench depth
- Plumbing inspections
About this tool
What the Drain Slope Calculator does
Gravity drains need a steady fall so waste flows and solids are carried along. Codes commonly require 1/4 inch per foot for drains of 2½ inches and smaller and 1/8 inch per foot for 3 inch and larger. Multiply the slope by the run length to find the total drop.
It also works as a drain slope grade calculator or a pipe fall calculator.
Formula
- Total drop = run length × slope per foot
- Grade % = slope (in per ft) ÷ 12 × 100
Worked example
Using the starting values in the calculator above:
| Input | Value |
|---|---|
| Pipe run length | 40 ft |
| Slope | 1/4 in per ft (about 2%) |
| Pipe diameter | 3 in |
| Result | Value |
|---|---|
| Total drop | 10.00 |
| Slope check | Meets the common minimum |
| Grade | 2.08% |
| Total drop | 0.83 |
How to read the result
Too steep can be a problem too: on very steep runs liquid outruns solids. Follow code limits and the designer’s plans.
Check the drop against available ceiling or trench depth before committing to a route.
For planning only. Electrical, gas and refrigerant work must follow current codes and be carried out or checked by a licensed professional.
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Questions
Questions about this tool
The things clients actually want to know — costs, timelines, ownership and what happens after launch.
Commonly 1/4 inch per foot for pipes 2½ inches and smaller and 1/8 inch per foot for 3 inches and larger, but follow local code.
About 2.08%.
At 1/4 inch per foot, 10 inches.
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