Laminar Pipe Friction Factor Calculator

Calculate Darcy and Fanning friction factors for fully developed laminar pipe flow.

fD = 64 / Re

Reynolds number Re

Enter valid values in all required fields.

What this formula means

For steady, fully developed laminar flow in a circular pipe, the Darcy friction factor depends only on Reynolds number. The simple 64/Re relation does not apply to turbulent flow or arbitrary noncircular ducts without modification.

Use the relation for low-speed viscous pipe flow, capillary systems, laboratory tubing, and pressure-loss checks. The result should be interpreted with consistent units and with the assumptions of the underlying model in mind.

Worked example

At Re = 1000, Darcy f = 0.064 and Fanning f = 0.016.

Applications

Use the relation for low-speed viscous pipe flow, capillary systems, laboratory tubing, and pressure-loss checks. It is also useful as an independent check when comparing hand calculations, laboratory measurements, simulations, or preliminary engineering estimates.

Assumptions and common mistakes

Important: Verify Re is below the laminar transition range and distinguish Darcy from Fanning friction factor conventions.

Use SI units unless the field label states otherwise. Keep significant figures appropriate to the accuracy of the inputs, and do not treat a simplified calculator as a replacement for codes, detailed design standards, or professional review.

Frequently asked questions

What equation does this calculator use?fD = 64 / Re. The calculator evaluates the displayed relationship using the values entered above.

Are the results unit-sensitive?Yes. The input labels use SI units so the displayed output follows the corresponding SI unit.

Can I use this for engineering design?Use it for learning and preliminary checks. Final designs require validated data, applicable standards, safety factors, and professional judgment.