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Laminar Friction Factor (f = 64/Re)

f=64Ref = \frac{64}{Re}

Units aren’t used in this calculation: every value is a plain number.

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Worked example: Re = 1600 → f = 0.04. Press Try an example to run it live, then adjust anything.

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Where Laminar Friction Factor (f = 64/Re) fits

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Darcy–Weisbach Head LossEquivalent Length of a Fitting
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See also

Swamee–Jain Friction Factor: Both use darcy friction factor and Reynolds number.Colebrook–White Friction Factor: Both use darcy friction factor and Reynolds number.Darcy–Weisbach Head Loss: Both use darcy friction factor.Equivalent Length of a Fitting: Both use darcy friction factor.Dittus-Boelter Correlation: Both use Reynolds number.Graetz Number: Both use Reynolds number.
1 more relatedReynolds Number: Both use Reynolds number.
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Laminar Friction Factor (f = 64/Re) explained

Ref

This is one of the few exact results in pipe hydraulics: integrate the parabolic Hagen–Poiseuille velocity profile and the Darcy friction factor falls out as precisely 64/Re, with no empirical fitting anywhere. At Re = 1600 that is f = 0.04. Because it is exact, it also anchors the left-hand edge of every Moody diagram ever drawn: the straight line of slope −1 on log-log paper that all the roughness curves eventually peel away from.

The striking implication is that roughness is irrelevant in laminar flow. A rusty pipe and a glass pipe give identical pressure drop, because the fluid nearest the wall is not moving and the flow never sees the bumps. Above Re ≈ 2300 the assumption collapses; in the 2300–4000 transition band no correlation is reliable and prudent engineers simply design out of it, usually by choosing a diameter that puts velocity solidly into turbulent territory.

Laminar Friction Factor (f = 64/Re) formula

f=64Ref = \frac{64}{Re}
Where
  • ff= Darcy friction factor
  • ReRe= Reynolds number
In this toolkit

Pipe friction losses

9 formulasDarcy–Weisbach, Hazen–Williams, friction factors, minor losses and equivalent length — every way the trade computes head loss in pipe.

Revised 31 October 2026
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formula.expert. (2026, October 31). Laminar Friction Factor (f = 64/Re) Formula & Calculator. https://formula.expert/solvers/friction-factor-laminar

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