Darcy Friction Factor Calculator Form
Use direct Reynolds input or compute Reynolds number from fluid properties. The form stays in a single vertical page flow, while inputs use a responsive grid.
Plotly Graph
The graph compares laminar, Churchill, and Colebrook behavior over a wide Reynolds number range using the current relative roughness value.
Formula Used
Reynolds number
Re = (ρ × V × D) / μ
Relative roughness
ε/D = absolute roughness / diameter
Laminar relation
f = 64 / Re
Colebrook-White equation
1/√f = -2 log10[(ε/3.7D) + 2.51/(Re√f)]
Swamee-Jain equation
f = 0.25 / [log10((ε/3.7D) + 5.74/Re^0.9)]²
Haaland equation
1/√f = -1.8 log10[((ε/3.7D)^1.11) + 6.9/Re]
Darcy-Weisbach pressure drop
ΔP = f × (L/D) × (ρV²/2)
Head loss
hf = f × (L/D) × (V²/2g)
Auto mode uses 64/Re for laminar flow, Churchill for transitional flow, and Colebrook-White for turbulent flow.
How to Use This Calculator
- Choose Fluid properties if you know velocity, density, viscosity, diameter, and roughness.
- Choose Direct Reynolds input if Reynolds number and relative roughness are already known.
- Select a method, or keep Auto for automatic regime handling.
- Enter all needed values and units.
- Press Calculate Friction Factor.
- Review the result section above the form.
- Inspect the graph and comparison table.
- Download the summary as CSV or PDF.
Example Data Table
These sample rows are illustrative and help users understand typical input-output behavior.
| Reynolds Number | Relative Roughness | Method | Darcy Friction Factor |
|---|---|---|---|
| 800 | 0.0000 | Laminar equation | 0.0800 |
| 3,000 | 0.0005 | Churchill | 0.0432 |
| 10,000 | 0.00045 | Haaland | 0.0317 |
| 50,000 | 0.00002 | Blasius | 0.0212 |
| 100,000 | 0.0020 | Colebrook-White | 0.0251 |
Frequently Asked Questions
1) What is the Darcy friction factor?
The Darcy friction factor is a dimensionless measure of internal wall friction. Engineers use it in the Darcy-Weisbach equation to estimate pressure loss and head loss in pipes.
2) Is Darcy friction factor the same as Fanning friction factor?
No. The Darcy friction factor equals four times the Fanning friction factor. Always confirm which convention your chart, textbook, or software is using.
3) When is the 64/Re equation valid?
The relation f = 64/Re is valid for fully developed laminar flow, generally when Reynolds number is below 2300 in a circular pipe.
4) Which method should I choose for turbulent flow?
Colebrook-White is a strong reference method for turbulent flow. Haaland and Swamee-Jain are faster explicit alternatives. Churchill is useful when you want one equation across all regimes.
5) Why does pipe roughness matter?
Rougher walls create more resistance, especially in turbulent flow. As Reynolds number rises, roughness often becomes more important than viscosity for friction factor behavior.
6) Why is transitional flow harder to model?
Transitional flow sits between laminar and turbulent behavior. Small disturbances can change the result, so different correlations may predict slightly different friction factors in this region.
7) Can this calculator estimate pressure drop too?
Yes. In fluid-properties mode, it also calculates pressure drop and head loss using the Darcy-Weisbach equation, pipe length, density, diameter, and flow velocity.
8) Which viscosity should I enter?
Enter dynamic viscosity in Pa·s or cP. If you only know kinematic viscosity, convert it first using μ = ρν before entering the value.