In typical engineering applications, there will be a set of given or known quantities. The acceleration of gravity  and the kinematic viscosity of the fluid  are known, as are the diameter of the pipe  and its roughness height . If as well the head loss per unit length  is a known quantity, then the friction factor  can be calculated directly from the chosen fitting function. Solving the Darcy–Weisbach equation for ,
we can now express :
Expressing the roughness Reynolds number ,
we have the two parameters needed to substitute into the Colebrook–White relation, or any other function, for the friction factor , the flow velocity , and the volumetric flow rate .