The drag of cross flow staggered and in-line helically and annularly finned tube bundles is investigated experimentally. The widest range of the reported geometric characteristics of finned tubes and tube bundles is considered. It is shown that when generalizing the experimental data obtained the best result is achieved by taking into account the Reynolds number exponent in the similarity equation as a function of geometric characteristics. Here as dimensionless parameters the geometric similarity of the reduced extended surface and the transverse-to-longitudinal tube pitch ratio are used, and also as the determining dimension in the Reynolds number - the equivalent diameter of the minimum flow section of the tube bundle. The results obtained by this approach describe with a sufficient accuracy 90% of all reported experimental data. (C) 2014 Elsevier Ltd. All rights reserved.