Compute the Darcy friction factor: laminar closed-form f=64/Re for Re<2000, or iterative Colebrook-White solution for transitional/turbulent flow, with the explicit Haaland approximation always returned as a cross-check. Reports relative roughness ε/D, absolute roughness (m), diameter (m), flow regime (laminar/transitional/turbulent), effective method and iteration count. Roughness ε in m/mm/µm, diameter D in m/cm/mm.
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Key facts
Category
Math & Numbers
Input types
number, select
Output type
json
Sample coverage
4
API ready
Yes
Overview
The Pipe Friction Factor Calculator computes the Darcy friction factor from Reynolds number, pipe roughness, and internal diameter. It uses f=64/Re for laminar flow and Colebrook-White iteration for higher Reynolds numbers, while also returning a Haaland estimate for comparison.
When to use
Estimate the Darcy friction factor for a pipe-flow calculation.
Compare iterative Colebrook-White and explicit Haaland results for turbulent flow.
Check how pipe roughness, diameter, and Reynolds number affect the flow regime and relative roughness.
How it works
1Enter a positive Reynolds number, absolute roughness, and internal pipe diameter.
2Select roughness and diameter units: m, mm, or µm for roughness, and m, cm, or mm for diameter.
3Choose Auto, Colebrook (iterative), or Haaland (explicit) as the calculation method.
4Review the Darcy friction factor, Haaland cross-check, relative roughness, flow regime, effective method, and iteration count.
Use cases
Pipe-flow and fluid-mechanics calculations requiring a Darcy friction factor.
Hydraulic comparisons between smooth and rough pipes using relative roughness.
Engineering checks that compare Colebrook-White results with the Haaland approximation.
Examples
1. Commercial-steel pipe at Re=100,000
Fluid systems engineer
Background
An engineer needs the Darcy friction factor for a commercial-steel pipe with known roughness and diameter.
Problem
Calculate the turbulent friction factor and compare the iterative result with the Haaland approximation.
How to use
Enter Reynolds number 100000, roughness 0.0457 mm, diameter 0.05 m, select Auto, and use 6 decimal places.
Re=100000; ε=0.0457 mm; D=0.05 m; Method=Auto; Decimal places=6
Outcome
The tool reports turbulent flow, relative roughness ε/D=0.000914, Colebrook friction factor f=0.021881, Haaland estimate 0.021664, and 10 iterations.
2. Smooth pipe at Re=10,000
Hydraulics student
Background
A student wants to verify the friction factor for a smooth pipe under turbulent-flow conditions.
Problem
Use zero roughness and compare the Colebrook-White result with the Haaland estimate.
How to use
Enter Reynolds number 10000, roughness 0 mm, diameter 0.1 m, select Auto, and use 6 decimal places.
FAQ
What does this calculator return?
It returns the Darcy friction factor, relative roughness, flow regime, effective method, and iteration count. A Haaland estimate is also provided as a cross-check.
Which formula is used for laminar flow?
For Re<2000, the calculator uses the closed-form relation f=64/Re.
How does Auto mode choose the method?
Auto uses the laminar formula when Re<2000 and Colebrook-White otherwise. The Haaland estimate is still reported for comparison.
Can I calculate friction for a smooth pipe?
Yes. Enter roughness as 0 to represent a perfectly smooth pipe.
What inputs are required?
Reynolds number, absolute roughness, and internal pipe diameter are required. Unit selections, method, and decimal places are optional.