The availability of wick drains has rapidly led to their replacing conventional sand drains as a means of accelerating the consolidation of soft soils. Wick drains have an oblong shape, but the available theories of radial consolidation have been derived for drains having a circular shape. What is needed to apply these theories to the design of field installations of wick drains is a method of calculating the equivalent diameter of an oblong shape. Previous investigators have suggested several equations for computing the equivalent diameter of wick drains, but they yield different results. The equivalent diameter of oblong drains is determined with an analog field plotter. The results of all methods are reviewed and then compared to published experimental values of equivalent diameters of wick drains. These values were determined from laboratory consolidation tests. Values of equivalent drain diameters backfigured from field data are discussed with respect to the influence of smear.