Skip to main content

    Drain slope Calc

    Minimum code-compliant fall over a horizontal run. Defaults to ¼″ per foot under 3″ diameter, ⅛″ per foot for 4″ and up.

    02Parameters
    Estimate only

    Results are estimates intended as a starting point. Verify against your project's specifics, manufacturer data, and applicable codes before relying on them. Use at your own risk. Read full terms.

    Relevant requirements

    No notes for this location/project. Always verify with your local authority.

    Frequently Asked Questions

    What is the minimum slope for a drain pipe?

    The IPC minimum is 1/4 inch per foot (2%) for pipe 2-1/2 inches and smaller. For 3-inch through 6-inch pipe the IPC allows 1/8 inch per foot (1%), and 1/16 inch per foot for 8-inch and larger, provided the design velocity stays at least 2 ft/s. The UPC is generally stricter, so check your adopted code and AHJ.

    Can a drain have too much slope?

    Yes. If a drain falls too steeply (well over 1/2 inch per foot), liquid can outrun the solids and leave them behind, causing clogs — the classic self-scouring concern. For long runs the goal is steady, uniform slope near 1/4 inch per foot rather than a steep drop followed by a flat section.

    What slope do I need for a 4-inch sewer line?

    A 4-inch building sewer under the IPC needs a minimum 1/8 inch per foot (1%), about 1 foot of fall per 100 feet, as long as the design maintains a 2 ft/s scouring velocity. Many jurisdictions and the UPC prefer 1/4 inch per foot for residential sewers — confirm with your local code before trenching.