What it does
Computes Darcy friction factor \(f_D\) and Fanning friction factor \(f_F = f_D/4\) using Colebrook–White (iterative) and explicit correlations (Haaland, Swamee–Jain, Serghide). Includes laminar \(f_D=64/\mathrm{Re}\), transitional flags, head-loss per length, ΔP over length, and a mini Moody chart.
Inputs
Results
Darcy friction factor \(f_D\)
—
Fanning friction factor \(f_F\)
—
Computed Reynolds number
—
Mean velocity \(V\)
—
m/s (if derivable)
Pressure drop per length ΔP/L
—
Head loss per length hf/L
—
ΔP over user length
—
hf over user length
—
If laminar: \(f_D = 64/\mathrm{Re}\). Transitional regime may be unstable; explicit methods differ.
Saved runs
| # | Method | Re | ε/D | fD | fF |
|---|
Use “Add to table” to store results for export.
Mini Moody chart
Curves from Swamee–Jain explicit formula; laminar line \(f_D=64/\mathrm{Re}\) shown. Marker updates from current inputs.
Example scenarios (precalculated)
| Scenario | Re | ε/D | Method | fD (approx) | fF (approx) |
|---|---|---|---|---|---|
| Smooth turbulent | 100000 | 0.0 | Haaland | 0.0183 | 0.00458 |
| Commercial steel | 150000 | 0.0003 | Serghide | 0.0211 | 0.00528 |
| Laminar | 1200 | 0.0000 | Laminar | 0.0533 | 0.01333 |
Formulas used
Colebrook–White (Darcy friction factor)
\\[ \\frac{1}{\\sqrt{f_D}} = -2\\log_{10}\\!\\left( \\frac{\\varepsilon/D}{3.7} + \\frac{2.51}{\\mathrm{Re}\\sqrt{f_D}} \\right) \\]
Solved iteratively with initial guess from explicit correlations.
Laminar flow
\\[ f_D = \\frac{64}{\\mathrm{Re}},\\quad f_F = \\frac{f_D}{4} \\]
Explicit correlations (Darcy)
Haaland: \\[ \\frac{1}{\\sqrt{f_D}} = -1.8\\log_{10}\\!\\left[ \\left(\\frac{\\varepsilon/D}{3.7}\\right)^{1.11} + \\frac{6.9}{\\mathrm{Re}} \\right] \\]
Swamee–Jain: \\[ f_D = \\frac{0.25}{\\left[\\log_{10}\\!\\left( \\frac{\\varepsilon/D}{3.7} + \\frac{5.74}{\\mathrm{Re}^{0.9}} \\right)\\right]^2} \\]
Serghide: Three-iteration explicit refinement for high accuracy.
Head-loss per length: \\[ \\frac{\\Delta P}{L} = f_D \\frac{\\rho V^2}{2D},\\quad \\frac{h_f}{L} = f_D \\frac{V^2}{2gD} \\]
How to use this calculator
- Choose Input mode: enter Reynolds number or compute it from flow, diameter, and kinematic viscosity.
- Use Pipe NPS and Schedule presets to auto-fill inner diameter for common steel pipes.
- Provide roughness via ε/D or choose a material preset and supply diameter to auto-compute ε/D.
- Select a method. Use Colebrook–White for highest fidelity; explicit formulas are fast for estimates.
- Optionally set density and gravity to obtain ΔP/L and hf/L. Enter L for total ΔP and head.
- Click Compute, then Add to table to collect runs for CSV or PDF export.
FAQs
The Darcy factor \(f_D\) is four times the Fanning factor \(f_F\): \(f_D=4f_F\). Head loss in Darcy–Weisbach uses \(f_D\); some literature and CFD packages report \(f_F\).
Using \(f_D\), diameter \(D\), mean velocity \(V\), density \(\rho\), and gravity \(g\): \(\Delta P/L = f_D \rho V^2/(2D)\); \(h_f/L = f_D V^2/(2gD)\). Velocity is derived from \(Q\) and \(D\), or from \(\mathrm{Re}\), \(ν\), and \(D\).
NPS ⅛″ to 24″ with Schedules 10, 40, and 80 where commonly used. You can edit the internal table to align with your catalog or standard.
No. Inputs in feet, gallons, or ft²/s are converted to SI for calculations and then converted back to the requested output units for display.
Yes. The schedule selector only sets inner diameter. Adjust the roughness preset or numeric ε to match your material, e.g., PVC or cast iron.