ESDU 77029 gives a method for calculating the pressure loss for single-phase gas or liquid incompressible Newtonian flow through a coil. By correlating data for friction factor taken from a wide range of sources in the literature@ four Reynolds number regimes were identified and defined within each of which an equation for friction factor as a function of Reynolds number and coil diameter/tube diameter ratio was established. Correction factors are provided to take into account variation of fluid properties across the cross-section and variations in surface roughness. The data are strictly applicable to helical coils@ but a method of using them for non-helical coils is suggested. Estimates of the accuracy of the prediction are included@ and a practical worked example illustrates the use of the data.