@wikipedia

Quantitative dimensionless measure  $//<![CDATA[ \begin{array}{l}f\end{array} //]]>$ of the friction forces between fluid pipe flow and inner pipe walls based on Darcy–Weisbach equation.

It depends on Reynolds number  $//<![CDATA[ \begin{array}{l}\rm Re\end{array} //]]>$ and roughness  $//<![CDATA[ \begin{array}{l}\epsilon\end{array} //]]>$  (see Fig. 1): $//<![CDATA[ \begin{array}{l}f =f({\rm Re}, \, \epsilon)\end{array} //]]>$.

In engineering practice one can use either Moody Chart or Darcy friction factor @model to estimate the actual value of Darcy friction factor .

See also

Physics / Fluid Dynamics / Pipe Flow Dynamics / Darcy–Weisbach equation 

[ Darcy friction factor Single-phase @model ] [ Darcy friction factor Multi-phase @model ]

[ Moody Chart ]

Reference

[1] https://gmallya.com/moodys-friction-factor-calculator/