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Storm Drain Pipe Capacity & Sizing

Size or check a full circular gravity conduit using Manning uniform-flow hydraulics with SI/US inputs.

Preliminary full-flow gravity-conduit hydraulics only. Required diameter is a continuous hydraulic minimum, not a catalog-size recommendation.
01

Hydraulic inputs

No hidden velocity or utilization criteria.

Scenario
Full-flow Manning inputs
02

Hydraulic result

Enter inputs and calculate.

Q

Ready for calculation

Leave selected diameter blank for sizing-only mode.

Methodology

Manning full-flow circular conduit

TOOL-005 uses Q = (1/n) A R^(2/3) S^(1/2). For a full circular conduit, A = πD²/4 and R = D/4.

Two calculation modes

Input guidance

Worked example

For D = 1.2 m, S = 0.01 and n = 0.013, full-flow capacity is approximately 3.898730279 m³/s and velocity is 3.447234420 m/s.

Interpretation and limitations

“Adequate” means only that selected full-flow Manning capacity is at least the supplied design flow. It is not a code-compliance verdict. The machine-readable status basis is full-flow-hydraulic-capacity-only. The required diameter is not a catalog-size recommendation. This tool does not model inlet control, outlet control, surcharge, hydraulic grade line, tailwater, junction losses, pressurized flow, structural design, cover requirements or commercial pipe-size availability.

Source

Manning provenance is registered as SRC-MANNING-FULL-PIPE-TOOL005-001.