Manning Equation for Drain Pipes

Calculate flow capacity in drainage pipes using Manning's equation for gravity flow systems.

Internal diameter of drain pipe.
inches
Pipe slope in inches per foot (1/4" = 0.25).
in/ft
Roughness: 0.009 (PVC/ABS), 0.011 (copper), 0.013 (cast iron), 0.015 (concrete).

Results

Capacity (Half Full)-GPM
Capacity (Full Flow)-GPM
Velocity (Half Full)-ft/s
References: Based on Manning's equation per UPC and IPC drainage design