What drain slope means
Drain slope is how much a horizontal drain pipe drops along its length, so waste flows by gravity without leaving solids behind.
Also called pipe pitch, fall.
Where it matters on a plumbing job
Too little slope leaves solids; too much lets water outrun them. Check it with a level on any repair you touch, and on remodels plan floor and ceiling depth around the drain fall before the framing is set.
What the model code says
- Horizontal drains 2 1/2 inches and smaller slope at least 1/4 unit in 12; drains 3 inches and larger slope at least 1/8 unit in 12. (IRC 2021, Chapter 30)
Check which code edition your building department enforces for drain slope before you quote.
What it costs
For drain slope, the closest koira.ai price is the sewer line replacement cost guide, near $3,300 for a typical job and $1,400 to $5,300 for most. The guide shows its sources and what moves the price. The drain slope calculator prices a job line by line.
Work it out
- Free calculator: Drain slope calculator
- Cost guide: Sewer line replacement cost
- Licensing: Plumbing license rules by state
- Tools, templates and guides: Free plumbing resources
Sources: 2021 International Residential Code, Chapter 30, Sanitary Drainage (ICC). Checked October 9, 2026.