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Hazen–Williams Flow-Capacity Calculator

Invert the Hazen–Williams relationship to estimate flow from diameter, length, C-factor, and available friction head.

Why it matters: A visible equation keeps the calculation boundary and user-entered criteria available for technical review.

User inputs

Enter field measurements

5 inputs
Select I-P or SI display units; convert the complete input set before calculating.
in or mmUse actual internal diameter.
ft or mStraight developed length for the entered friction head.
dimensionlessUser-selected coefficient from an approved source.
ft or mHead allocated to the evaluated pipe length.

Calculated result

Engineering evaluation

Calculation complete—verify project criteria
Hazen–Williams flow screen (Q)102.734 gpm
Mean pipe velocity (v)
10.492 ft/s

Engineering interpretation

The entered diameter, length, C-factor, and friction-head allowance produce 102.7342 gpm.

Important limitations

  • The Hazen–Williams result is not a pipe-size selection. Verify actual internal diameter, C-factor basis, fittings and devices, velocity criteria, pressure transients, code requirements, and the complete critical path.

Engineering knowledge center

Understand the calculation—not just the answer

2026-08-07 · Free Library
Governing relationships
Q=[h_f C^1.85 d^4.87/(4.52L)]^(1/1.85) using I-P equation units
displayed symbols: D_i, v
Current substitution

Q=[10×130^1.85×2^4.87/(4.52×100)]^(1/1.85)=102.7342 gpm.

Calculation sequence

Step-by-step method

  1. Confirm the input boundary, formula symbols, and unit system.
  2. Apply the displayed equation to the user-entered values.
  3. Compare the screening result with project criteria, manufacturer data, and applicable standards.

Equation legend

Inputs and calculated quantities

D_i
Actual inside diameter — in or mm
L
Developed pipe length — ft or m
C
Hazen–Williams coefficient — dimensionless
h_f
Available friction head — ft or m
Q
Hazen–Williams flow screen — gpm
v
Mean pipe velocity — ft/s

Continue the evaluation

Related calculators

Hazen–Williams Pipe Loss Pipe Flow & Velocity Water Loss Budget

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