Drain Pipe Slope Calculator
Figure the minimum slope and total fall for a horizontal drain run straight from IPC Table 704.1 — and check whether the drop you can actually hit passes code.
IPC: ¼″ per ft for 2½″ and smaller
End of run to end of run, level
Elevation change you can hit
Min slope required¼″ per ft
Slope as % / angle2.08% · 1.2°
Drop per 10 ft2.5″
Min total drop over 10 ft2.5″
Set the pipe to one uniform slope for the whole run — sags and humps trap solids even when the average is fine. If your drop check fails, re-route, re-grade, or use a smaller pipe size where the run allows it.
Values are IPC Table 704.1 minimums (2021 edition; identical in 2018 and 2024): ¼″ per ft for 2½″ and smaller, ⅛″ per ft for 3″–6″, 1/16″ per ft for 8″ and larger. UPC jurisdictions use a slightly different cutoff (¼″ on 2″ and smaller, ⅛″ on 3″ and larger) — confirm the code your AHJ adopts. Steeper than minimum is fine and usually better; just keep it uniform.