Why use Darcy friction factor instead of Fanning?

The Moody chart and Darcy-Weisbach head-loss equation usually use the Darcy factor. The Fanning factor is one quarter of the Darcy factor, so mixing conventions causes a factor-of-four error.

What happens in the transition region?

Between roughly Re = 2300 and 4000, flow can switch between laminar and turbulent depending on disturbances and inlet conditions. The simulator flags it rather than pretending the correlation is precise there.

Pipe Friction & Moody Chart

Reynolds number, relative roughness, Swamee-Jain/Colebrook-style friction factor, and Darcy-Weisbach head loss.

This is a steady, fully developed pipe-flow model using Darcy friction factor. Minor losses, fittings, pumps, non-Newtonian fluids, compressibility, entrance effects, and two-phase flow are not included.

Live graphs

About this model

Pipe pressure loss in steady internal flow is commonly estimated with the Darcy-Weisbach equation, h_f = f(L/D)V²/(2g). The friction factor f depends on Reynolds number Re = ρVD/μ and relative roughness ε/D. This simulator uses f = 64/Re for laminar flow and the explicit Swamee-Jain approximation for turbulent flow, which tracks the Colebrook/Moody chart without iteration. The chart shows smooth and rough turbulent curves, transition markers, the current operating point, head loss, and pressure drop. It assumes steady, fully developed, incompressible, single-phase Newtonian flow in a straight circular pipe.

Who it's for: Fluid mechanics, hydraulics, HVAC, process piping, civil engineering, and mechanical engineering introductions.

Key terms

Moody chart
Darcy-Weisbach
Friction factor
Reynolds number
Relative roughness

How it works

Moody chart and Darcy-Weisbach pipe friction calculator: Reynolds number, relative roughness, Swamee-Jain friction factor, head loss, and pressure drop.

Key equations

Re = ρVD/μ, h_f = f (L/D) V²/(2g)

Swamee-Jain: f = 0.25/[log10(ε/(3.7D)+5.74/Re^0.9)]²; laminar f=64/Re

Frequently asked questions

Why use Darcy friction factor instead of Fanning?: The Moody chart and Darcy-Weisbach head-loss equation usually use the Darcy factor. The Fanning factor is one quarter of the Darcy factor, so mixing conventions causes a factor-of-four error.
What happens in the transition region?: Between roughly Re = 2300 and 4000, flow can switch between laminar and turbulent depending on disturbances and inlet conditions. The simulator flags it rather than pretending the correlation is precise there.

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About this model

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Key equations

Frequently asked questions

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Frequently asked questions