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Fanning Friction Factor in Conduits Equation and Calculator

Fluids Flow Design and Engineering
Hydraulic & Pneumatic Design Engineering

Fanning Friction Factor for Flow in Conduits Equation and Calculator

The Fanning friction factor is not the same as the Darcy Friction factor (which is 4 times greater than the Fanning Friction factor). The formula given is very similar to the Darcy-Weisbach formula but the Hydraulic Radius of the pipe work must used, not the pipe diameter.

Published tables of Fanning friction factors are usually only applicable to the turbulent flow of water at 60º F (15.5º C).

Eq. 1
For flow in conduits
f = 0.25 ( D / L ) [ ( P_o - P_L ) / ( 0.5 ρ v²) ]

D = Conduit Diameter (ft)
L = Length of conduit (ft)
P_o = Pressure initial (lbs / ft²)
P_L = Pressure output (lbs / ft²)
v = Flow Velocity (ft/s)
ρ = Fluid Density (g/cc)
f = Fanning Friction Factor (dimensionless)

Eq. 2
Fanning’s friction factor (turbulent flow)
f = ( 0.0791 µ^0.25 ) / ( D v ρ )^0.25

Where:

D = Conduit Diameter (ft)
v = Flow Velocity (ft/s)
ρ = Fluid Density (g/cc)
µ = viscosity ( [lbf s/ft²)
0.0791 = conversion
f = Fanning Friction Factor (dimensionless)

• Bird, R.B., Stewart, W.E. and Lightfoot, E.N. (2002). Transport Phenomena (Second Ed.). John Wiley & Sons, Chapter: 6, Page: 181.

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