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

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

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

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.

Other simulators in this category — or see all 46.

View category →

NewSchool

Open-Channel Flow & Hydraulic Jump

Rectangular-channel Froude number, critical depth, conjugate depths, energy loss, and subcritical/supercritical regimes.

Launch Simulator

NewSchool

Multilayer Wall Conduction

Three layers in series: R″ = L/k, q″ and U; T(x) sketch and preset plaster/brick/wool.

Launch Simulator

NewSchool

Adiabatic Cloud Parcel

Lift moist air: dry Γ, LCL, toy moist lapse; RH and cartoon cloud vs height.

Launch Simulator

NewSchool

Engine Cycles Compared (P–V)

One canvas: Carnot, Otto, Diesel, Stirling, Rankine sketch — switch cycles, same formulas as standalone labs.

Launch Simulator

NewSchool

Diesel Cycle (PV)

Air-standard: adiabat compress, isobaric heat, adiabat expand, isochoric out; η(ρ_c, β).

Launch Simulator

NewUniversity / research

Maxwell’s Demon (Toy)

2D billiards + gate: fast |v| crosses; ⟨|v|⟩ left/right + Landauer note.

Launch Simulator

Pipe Friction & Moody Chart

Live graphs

How it works

Key equations

Frequently asked questions

More from Thermodynamics

Open-Channel Flow & Hydraulic Jump

Multilayer Wall Conduction

Adiabatic Cloud Parcel

Engine Cycles Compared (P–V)

Diesel Cycle (PV)

Maxwell’s Demon (Toy)

Pipe Friction & Moody Chart

Live graphs

How it works

Key equations

Frequently asked questions