"blasius" Friction factor I am trying to find out if the formula below can be used to estimate the friction factor for turbulent flows with Reynolds number around 100,000, in an air system. f = 0.079*RE^-0.25 I have not been able to find this exact formula anywhere other than on this website http://www.seykota.com/rm/friction/friction.htm which states that it is valid for 4000<Re<100000. The above formula has been called the "blasius equation" so maybe it has been derived from it in some way? I think that if this formula works it cant be that accurate. Does anyone know where this comes from? Or prove it?