Backwater Valve Sizing Calculator

Size backwater valve based on pipe diameter, flow rate, and pipe slope

Nominal diameter of the building drain or sewer lateral where the backwater valve will be installed.
Maximum expected drainage flow. Use fixture unit conversion or measured flow.
GPM
Slope of the drain pipe, per code minimum is typically 1/8" to 1/4" per foot.

Results

Recommended Valve Size-inches
Pipe Capacity (Manning)-GPM
Flow Velocity-ft/s
Capacity Status-
References: Manning's equation for gravity flow (n=0.013 for PVC/smooth pipe). IPC/UPC backwater valve sizing requirements.