Plumbing & Fluid
Friction Factor Calculator
Compare Darcy and Fanning friction factors from Reynolds number and relative roughness. Compare SI/US results and review the method, assumptions and related references below.
Change any input to update the calculation. Unit changes preserve the physical quantity.
Inputs
Calculated locally in your browser. No sign-up or input upload.
Results
Darcy friction factor
0.0218Fanning friction factor
0.0055Relative roughness ε/D
0.0009Haaland / regime-model comparison
0.0216Approximation difference
-1.0009 %Calculation breakdown
- Result interpretation
- Compare Darcy and Fanning friction factors from Reynolds number and relative roughness
Assumptions & checks
Full circular-pipe Newtonian flow only. Transition is uncertain; below Re 4000 the comparison repeats the regime model instead of presenting a turbulent approximation.
Formula
Compare Darcy and Fanning friction factors from Reynolds number and relative roughness
Worked example
Using the default values shown in the calculator, the same formula gives the following result. This is a quick sanity check for the calculation, not a design recommendation.
Inputs
- Reynolds number
- 100000
- Actual inside diameter
- 50 mm
- Absolute roughness
- 0.045 mm
Result
- Darcy friction factor
- 0.0218
- Fanning friction factor
- 0.0055
- Relative roughness ε/D
- 0.0009
- Haaland / regime-model comparison
- 0.0216
- Approximation difference
- -1.0009 %
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Technical references for this calculation
Frequently asked questions
What does this result tell me?
Full circular-pipe Newtonian flow only. Transition is uncertain; below Re 4000 the comparison repeats the regime model instead of presenting a turbulent approximation.
How can I check the calculation?
Worked example: At Re=1000, the Darcy factor is 0.064 and the Fanning factor is 0.016, independent of entered roughness in the laminar model. Review each stated input and unit; use project-specific values rather than treating the editable example as a requirement.
Reference data & method sources
- US EPA EPANET 2.2 manual
Darcy-Weisbach, Reynolds-dependent friction and minor-loss K methods for full circular pipe.
- NIST SI conversion factors
SI/US dimensional conversions. Geometry and energy balances are stated explicitly, not attributed to a design standard.