PIPE SLOPE
PIPE SLOPE
drop = run × slope/ft
ft
RESULT
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FILL IN ABOVE
IPC/UPC: 1/4"/ft for ≤2.5" pipe, 1/8"/ft for 3"+. Don't exceed 1/2"/ft.
About this calculator
This pipe slope calculator gives the total drop and grade percent for a drain or sewer line. The IPC and UPC plumbing codes require a minimum 1/4" per foot fall on horizontal drains 2.5" and smaller, and 1/8" per foot on 3" and larger pipe (some jurisdictions allow 1/16" per foot on 8"+ pipe with engineering approval). Too little slope and solids settle out of the flow; too much (above 1/2" per ft) and water outruns the solids — both end the same way, with a clog.
Common questions
What is the minimum slope for a 2-inch drain?
1/4" per foot (about a 2% grade) per IPC and UPC. That's the standard for any horizontal drain 2.5 inches and smaller — kitchen, lavatory, shower, washing machine. Sloping less risks solids settling out and clogging the line.
Can a drain pipe have too much slope?
Yes. Above about 1/2" per foot, water flows faster than the solids it's carrying, leaving them behind to build up on the pipe walls. The clog pattern looks identical to too-little slope. The sweet spot is 1/4"/ft for small pipe, 1/8"/ft for 3"+ mains.
Does this apply to vent pipes?
Vent pipes only need to slope back toward the drain so condensation drains out — exact pitch isn't code-critical. The drain-side rules are what matters for waste flow. For sewer mains, also confirm your local jurisdiction's amendments — some cities tighten the IPC defaults.