Free Drainage Slope Calculator
Calculate the required drop in elevation over a given run to achieve the correct drainage slope for waste pipes.
ft
Total Drop
5.00 in
Total Drop0.417 ft
Slope Percentage2.08 %
Total Drop vs Pipe Run Length
Drainage Slope
Total Drop = Run Length x Slope
The standard slope for most residential drain lines (3-inch and larger) is 1/4 inch per foot. Pipes smaller than 3 inches often require 1/4 in/ft as well, though codes may specify 1/8 in/ft for larger commercial mains.
Example Calculation
A 20-foot drain run at the standard 1/4 in/ft slope.
- 01Drop = 20 x 0.25 = 5 inches
- 02In feet = 5 / 12 = 0.417 ft
- 03The outlet must be 5 inches lower than the inlet.
Frequently Asked Questions
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