ESDU 79034 gives a method derived from ESDU 74040 that greatly simplifies the prediction of pressure loss for tube lay-outs typical of shell-and-tube heat exchanger design, that is with tubes in-line or staggered in either square or equilateral triangular lay-out. The method applies to tube pitch/diameter ratios of 1.2 to 3 and superficial Reynolds numbers (that is based on a flow velocity calculated on a flow area that neglects the area occupied by the tube) of one to a million based on tube diameter. Equations are given for a loss coefficient as a function of the pitch/diameter ratio and superficial Reynolds number for each of the four cases, and graphs of the curves are included. Correction factors are also given to correct values of the loss coefficient for the effects of viscosity variation due to temperature, flow inclination to the tube, and surface roughness of the tube. A comprehensive worked example illustrates the use of the data.