Darcy Friction Factor

Fluid & Pressure

Darcy friction factor: 64/Re when laminar, Haaland when Re ≥ 2300.

App id: FLUID-06. Reference version 1.0.

How to fill it

Fill the inputs. The tool shows the outputs.

On the tool screen, Calc is the working sheet. Presets stores values you reuse. Reference is the formula, assumptions, and provenance below.

Formula

laminar f = 64/Re; turbulent 1/√f = −1.8 log10[(ε/(3.7D))^1.11 + 6.9/Re]

Inputs

Name	Unit
Reynolds number	`1`
Inside diameter	`mm`
Absolute roughness (optional)	`mm`

Outputs

Name	Unit
Darcy friction factor (hero result)	`1`
Relative roughness ε/D	`1`

Diagnose

Observations are context. They do not pass or fail a structure. See Diagnose.

Screening bands in the app: Laminar · Transitional · Turbulent.

When	Observation	Severity
`Reynolds number < 2300`	Laminar	info
`Reynolds number ≤ 4000`	Transitional	caution
`Reynolds number > 4000`	Turbulent	info
`relative > 0.05`	Very high relative roughness	caution

Assumptions

Darcy factor, not Fanning.
Leave roughness blank for a smooth pipe (ε = 0).
Transitional Re uses the Haaland branch.

Provenance

Haaland, S. E. (1983). Simple and explicit formulas for the friction factor in turbulent pipe flow.