Calculation sequence
Step-by-step method
- Confirm the calculation boundary, units, and source of every input.
- Apply the displayed equation to the entered values.
- Review the result against governing criteria and documented uncertainty.
PlumbingAdvancedSanitary and Storm Drainage
Part-Full Circular-Pipe Manning Calculator
Calculate part-full circular-pipe flow from depth ratio, diameter, slope, and Manning roughness.
Why it matters: A transparent formula keeps the user-entered hydraulic, gas, or storage basis available for technical review.
Calculated result
Engineering evaluation
Part-full gravity flow (Q)799.549 gpm
- Flow area (A)
- 0.393 ft²
- Hydraulic radius (R_h)
- 0.25 ft
- Mean velocity (v)
- 4.536 ft/s
Engineering interpretation
At y/D=0.5, the entered Manning basis yields 799.5489 gpm.
Important limitations
- Uniform part-full circular flow only. Do not use as a protected code sizing table; verify slope, roughness, depth criterion, surcharge, venting, backwater, and local losses.
Engineering knowledge center
Understand the calculation—not just the answer
Governing relationships
θ=2acos(1−2y/D)
A=D²(θ−sinθ)/8
P=Dθ/2
R_h=A/P
Q=(K/n)AR_h^(2/3)S^(1/2)
displayed symbols: v
Current substitution
θ=3.141593 rad; A=0.3926991; R_h=0.25; Q=799.5489 gpm.
Equation legend
Inputs and calculated quantities
- D
- Pipe inside diameter — in or m
- y/D
- Flow-depth ratio — 0–1
- S
- Hydraulic slope — ft/ft or m/m
- n
- Manning roughness — dimensionless
- Q
- Part-full gravity flow — gpm
- A
- Flow area — ft²
- R_h
- Hydraulic radius — ft
- v
- Mean velocity — ft/s
Applications
How this calculation is used
Building design
Screen a documented system relationship without embedding a protected design table.
Construction
Check submittal and field values using the same visible inputs.
Commissioning
Reconcile measured and scheduled conditions before professional disposition.
Quality controls
Assumptions and limitations
Assumptions
- Inputs describe one documented system boundary and compatible operating condition.
- All values use the displayed symbols and one consistent unit system.
Limitations
- This screen does not establish code compliance, final design, equipment selection, or acceptance.
- Adopted codes, local criteria, manufacturer data, uncertainty, and professional judgment remain controlling.
Field use
Verification procedure
- Identify the calculation boundary and source of each input.
- Record representative values with compatible pressure, temperature, flow, and time bases.
- Review the result against the adopted criteria, manufacturer data, and uncertainty.
Common engineering mistakes
- Mixing standard and actual gas volumes or gauge and absolute pressures.
- Treating an arithmetic screen as a code-sizing table or hidden acceptance criterion.
Technical basis
References and source standards
- International Plumbing CodeAdopted edition and local amendments govern; protected sizing tables are not reproduced.
- American Society of Plumbing EngineersPlumbing engineering-method context; verify licensed references and project criteria.
- NIST SI and Unit GuidanceUnit and dimensional-conversion basis.
Engineering calculation disclaimer
These engineering tools are provided for educational, preliminary evaluation, field verification, and commissioning support. Results depend on the accuracy of user-entered information and the assumptions stated for each calculation. Every colored status and comparison is a screening indicator only; project criteria, contract requirements, applicable codes, manufacturer instructions, measurement uncertainty, and authorized engineering judgment govern. The tools do not replace project-specific engineering analysis or the judgment of a licensed professional engineer.
Read the full use and limitation statement