Pipe Capacity Calculator
Estimate full-flow capacity for a circular pipe using diameter, slope, and Manning roughness.
Pipe Capacity Calculator
Estimate full-flow pipe capacity, velocity, area, wetted perimeter, and hydraulic radius.
What this calculator assumes
This screening calculator assumes a circular pipe flowing full using Manning equation. It does not check inlet control, outlet control, surcharging, backwater, losses, or pressure flow.
Use for quick planning checks only. Detailed design may require modeling or local agency methods.
What this calculator does
This tool estimates the capacity of a circular pipe flowing full using Manning equation. It reports flow capacity, velocity, area, and hydraulic radius.
Inputs explained
- Pipe diameter: The inside diameter of the pipe.
- Slope: The pipe slope or energy grade slope used in the Manning calculation.
- Manning n: A roughness coefficient representing pipe material and condition.
Limitations
This is a full-flow screening check. It does not evaluate inlet control, outlet control, culvert hydraulics, surcharge, pressure flow, tailwater, bends, junction losses, or local storm drain criteria.
FAQ
Is this the same as culvert capacity?
No. Culvert capacity may be governed by inlet control, outlet control, tailwater, entrance losses, and roadway overtopping.
What Manning n should I use?
Use the value required by the local agency or the pipe manufacturer. New smooth pipe normally uses a lower n than older rough pipe.
Does this calculate partial pipe flow?
No. Use the Manning Equation Calculator for open-channel and partially full pipe checks.
Can this be used for final storm drain design?
Use it for early checks only. Final design should follow the local drainage manual and required modeling methods.
Related tools
Need help reviewing this result?
Use this calculator for planning-level checks, then request help if you need a second look at assumptions, units, stormwater criteria, pump sizing, storage volume, or report-ready calculations.