Darcy-Weisbach vs Hazen-Williams: Which to Use

The two most common pipe friction models in engineering practice are Darcy-Weisbach (using the Colebrook-White friction factor) and Hazen-Williams (an empirical C-factor formula). This guide explains how each works, where they agree, and where they diverge in accuracy and applicability.

Darcy-Weisbach is the rigorous standard. It is valid for any Newtonian fluid - water, oil, gas, refrigerants - across laminar, transitional, and turbulent flow. It requires viscosity as an input and an iterative solution of the Colebrook-White equation for the friction factor, but it is the most accurate general-purpose method available for engineering calculations.

Hazen-Williams is simpler: a single C-factor characterises pipe roughness, and the formula is non-iterative. It is the industry standard for municipal water distribution and remains widely used in fire-protection design. The trade-off is scope - Hazen-Williams is only valid for water at typical service temperatures and turbulent flow. For compressible gas, oils, refrigerants, or any fluid outside that empirical envelope, use Darcy-Weisbach.

Try both methods side-by-side with our free friction loss calculator, or check pipe sizing under either model in the SimuPipe editor.

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